linux-surface/patches/5.8/0002-surface-sam.patch

From 0be98f240951d46cc8871a777d47a7d502d03305 Mon Sep 17 00:00:00 2001
From: Maximilian Luz <luzmaximilian@gmail.com>
Date: Fri, 6 Dec 2019 11:56:12 +0100
Subject: [PATCH 2/5] surface-sam

---
 drivers/platform/x86/Kconfig                  |    2 +
 drivers/platform/x86/Makefile                 |    1 +
 drivers/platform/x86/surface_sam/Kconfig      |  176 +
 drivers/platform/x86/surface_sam/Makefile     |   16 +
 .../x86/surface_sam/surface_sam_debugfs.c     |  270 +
 .../x86/surface_sam/surface_sam_dtx.c         |  582 ++
 .../x86/surface_sam/surface_sam_hps.c         | 1287 ++++
 .../x86/surface_sam/surface_sam_san.c         |  930 +++
 .../x86/surface_sam/surface_sam_san.h         |   30 +
 .../x86/surface_sam/surface_sam_sid.c         |  283 +
 .../x86/surface_sam/surface_sam_sid_gpelid.c  |  232 +
 .../surface_sam/surface_sam_sid_perfmode.c    |  214 +
 .../x86/surface_sam/surface_sam_sid_power.c   | 1054 ++++
 .../x86/surface_sam/surface_sam_sid_power.h   |   16 +
 .../x86/surface_sam/surface_sam_sid_vhf.c     |  429 ++
 .../x86/surface_sam/surface_sam_sid_vhf.h     |   14 +
 .../x86/surface_sam/surface_sam_ssh.c         | 5329 +++++++++++++++++
 .../x86/surface_sam/surface_sam_ssh.h         |  717 +++
 .../x86/surface_sam/surface_sam_ssh_trace.h   |  587 ++
 .../x86/surface_sam/surface_sam_vhf.c         |  266 +
 20 files changed, 12435 insertions(+)
 create mode 100644 drivers/platform/x86/surface_sam/Kconfig
 create mode 100644 drivers/platform/x86/surface_sam/Makefile
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_debugfs.c
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_dtx.c
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_hps.c
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_san.c
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_san.h
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_sid.c
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_sid_gpelid.c
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_sid_perfmode.c
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_sid_power.c
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_sid_power.h
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_sid_vhf.c
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_sid_vhf.h
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_ssh.c
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_ssh.h
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_ssh_trace.h
 create mode 100644 drivers/platform/x86/surface_sam/surface_sam_vhf.c

diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
index 0581a54cf562..998007444059 100644
--- a/drivers/platform/x86/Kconfig
+++ b/drivers/platform/x86/Kconfig
@@ -1376,6 +1376,8 @@ config INTEL_SCU_PLATFORM
 	  and SCU (sometimes called PMC as well). The driver currently
 	  supports Intel Elkhart Lake and compatible platforms.
 
+source "drivers/platform/x86/surface_sam/Kconfig"
+
 config INTEL_SCU_IPC_UTIL
 	tristate "Intel SCU IPC utility driver"
 	depends on INTEL_SCU
diff --git a/drivers/platform/x86/Makefile b/drivers/platform/x86/Makefile
index 2b85852a1a87..e154e679db45 100644
--- a/drivers/platform/x86/Makefile
+++ b/drivers/platform/x86/Makefile
@@ -148,3 +148,4 @@ obj-$(CONFIG_INTEL_TELEMETRY)		+= intel_telemetry_core.o \
 					   intel_telemetry_pltdrv.o \
 					   intel_telemetry_debugfs.o
 obj-$(CONFIG_PMC_ATOM)			+= pmc_atom.o
+obj-$(CONFIG_SURFACE_SAM)	+= surface_sam/
diff --git a/drivers/platform/x86/surface_sam/Kconfig b/drivers/platform/x86/surface_sam/Kconfig
new file mode 100644
index 000000000000..b5bb55248a5d
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/Kconfig
@@ -0,0 +1,176 @@
+menuconfig SURFACE_SAM
+	depends on ACPI
+	tristate "Microsoft Surface/System Aggregator Module and Platform Drivers"
+	help
+	  Drivers for the Surface/System Aggregator Module (SAM) of Microsoft
+	  Surface devices.
+
+	  SAM is an embedded controller that provides access to various
+	  functionalities on these devices, including battery status, keyboard
+	  events (on the Laptops) and many more.
+
+	  Say M/Y here if you have a Microsoft Surface device with a SAM device
+	  (i.e. 5th generation or later).
+
+config SURFACE_SAM_SSH
+	tristate "Surface Serial Hub Driver"
+	depends on SURFACE_SAM
+	depends on SERIAL_DEV_CTRL_TTYPORT
+	select CRC_CCITT
+	default m
+	help
+	  Surface Serial Hub driver for 5th generation (or later) Microsoft
+	  Surface devices.
+
+	  This is the base driver for the embedded serial controller found on
+	  5th generation (and later) Microsoft Surface devices (e.g. Book 2,
+	  Laptop, Laptop 2, Pro 2017, Pro 6, ...). This driver itself only
+	  provides access to the embedded controller (SAM) and subsequent
+	  drivers are required for the respective functionalities.
+
+	  If you have a 5th generation (or later) Microsoft Surface device, say
+	  Y or M here.
+
+config SURFACE_SAM_SSH_ERROR_INJECTION
+	bool "Surface Serial Hub Error Injection Capabilities"
+	depends on SURFACE_SAM_SSH
+	depends on FUNCTION_ERROR_INJECTION
+	default n
+	help
+	  Enable error injection capabilities for the Surface Serial Hub.
+	  This is used to debug the driver, specifically the communication
+	  interface. It is not required for normal use.
+
+	  If you are not sure, say N here.
+
+config SURFACE_SAM_DEBUGFS
+	tristate "Surface Serial Hub Debug Device"
+	depends on SURFACE_SAM_SSH
+	depends on DEBUG_FS
+	default n
+	help
+	  Debug device for direct communication with the embedded controller
+	  found on 5th generation (and later) Microsoft Surface devices (e.g.
+	  Book 2, Laptop, Laptop 2, Pro 2017, Pro 6, ...) via debugfs.
+
+	  If you are not sure, say N here.
+
+config SURFACE_SAM_SAN
+	tristate "Surface ACPI Notify Driver"
+	depends on SURFACE_SAM_SSH
+	default m
+	help
+	  Surface ACPI Notify driver for 5th generation (or later) Microsoft
+	  Surface devices.
+
+	  This driver enables basic ACPI events and requests, such as battery
+	  status requests/events, thermal events, lid status, and possibly more,
+	  which would otherwise not work on these devices.
+
+	  If you are not sure, say M here.
+
+config SURFACE_SAM_VHF
+	tristate "Surface Virtual HID Framework Driver"
+	depends on SURFACE_SAM_SSH
+	depends on HID
+	default m
+	help
+	  Surface Virtual HID Framework driver for 5th generation (or later)
+	  Microsoft Surface devices.
+
+	  This driver provides support for the Microsoft Virtual HID framework,
+	  which is required for keyboard support on the Surface Laptop 1 and 2.
+
+	  If you are not sure, say M here.
+
+config SURFACE_SAM_DTX
+	tristate "Surface Detachment System (DTX) Driver"
+	depends on SURFACE_SAM_SSH
+	depends on INPUT
+	default m
+	help
+	  Surface Detachment System (DTX) driver for the Microsoft Surface Book
+	  2. This driver provides support for proper detachment handling in
+	  user-space, status-events relating to the base and support for
+	  the safe-guard keeping the base attached when the discrete GPU
+	  contained in it is running via the special /dev/surface-dtx device.
+
+	  Also provides a standard input device to provide SW_TABLET_MODE events
+	  upon device mode change.
+
+	  If you are not sure, say M here.
+
+config SURFACE_SAM_HPS
+	tristate "Surface dGPU Hot-Plug System (dGPU-HPS) Driver"
+	depends on SURFACE_SAM_SSH
+	depends on SURFACE_SAM_SAN
+	depends on GPIO_SYSFS
+	default m
+	help
+	  Driver to properly handle hot-plugging and explicit power-on/power-off
+	  of the discrete GPU (dGPU) on the Surface Book 2 and 3.
+
+	  If you are not sure, say M here.
+
+config SURFACE_SAM_SID
+	tristate "Surface Platform Integration Driver"
+	depends on SURFACE_SAM_SSH
+	default m
+	help
+	  Surface Platform Integration Driver for the Microsoft Surface Devices.
+	  This driver loads various model-specific sub-drivers, including
+	  battery and keyboard support on 7th generation Surface devices, proper
+	  lid setup to enable device wakeup when the lid is opened on multiple
+	  models, as well as performance mode setting support on the Surface
+	  Book 2.
+
+	  If you are not sure, say M here.
+
+config SURFACE_SAM_SID_GPELID
+	tristate "Surface Lid Wakeup Driver"
+	depends on SURFACE_SAM_SID
+	default m
+	help
+	  Driver to set up device wake-up via lid on Intel-based Microsoft
+	  Surface devices. These devices do not wake up from sleep as their GPE
+	  interrupt is not configured automatically. This driver solves that
+	  problem.
+
+	  If you are not sure, say M here.
+
+config SURFACE_SAM_SID_PERFMODE
+	tristate "Surface Performance Mode Driver"
+	depends on SURFACE_SAM_SID
+	depends on SYSFS
+	default m
+	help
+	  This driver provides support for setting performance-modes on Surface
+	  devices via the perf_mode sysfs attribute. Currently only supports the
+	  Surface Book 2. Performance-modes directly influence the fan-profile
+	  of the device, allowing to choose between higher performance or
+	  quieter operation.
+
+	  If you are not sure, say M here.
+
+config SURFACE_SAM_SID_VHF
+	tristate "Surface SAM HID Driver"
+	depends on SURFACE_SAM_SID
+	depends on HID
+	default m
+	help
+	  This driver provides support for HID devices connected via the Surface
+	  SAM embedded controller. It provides support for keyboard and touchpad
+	  on the Surface Laptop 3 models.
+
+	  If you are not sure, say M here.
+
+config SURFACE_SAM_SID_POWER
+	tristate "Surface SAM Battery/AC Driver"
+	depends on SURFACE_SAM_SID
+	select POWER_SUPPLY
+	default m
+	help
+	  This driver provides support for the battery and AC on 7th generation
+	  Surface devices.
+
+	  If you are not sure, say M here.
diff --git a/drivers/platform/x86/surface_sam/Makefile b/drivers/platform/x86/surface_sam/Makefile
new file mode 100644
index 000000000000..89bced46ebcd
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/Makefile
@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+# For include/trace/define_trace.h to include surface_sam_ssh_trace.h
+CFLAGS_surface_sam_ssh.o = -I$(src)
+
+obj-$(CONFIG_SURFACE_SAM_SSH)		+= surface_sam_ssh.o
+obj-$(CONFIG_SURFACE_SAM_SAN)		+= surface_sam_san.o
+obj-$(CONFIG_SURFACE_SAM_DTX)		+= surface_sam_dtx.o
+obj-$(CONFIG_SURFACE_SAM_HPS)		+= surface_sam_hps.o
+obj-$(CONFIG_SURFACE_SAM_VHF)		+= surface_sam_vhf.o
+obj-$(CONFIG_SURFACE_SAM_SID)		+= surface_sam_sid.o
+obj-$(CONFIG_SURFACE_SAM_SID_GPELID)	+= surface_sam_sid_gpelid.o
+obj-$(CONFIG_SURFACE_SAM_SID_PERFMODE)	+= surface_sam_sid_perfmode.o
+obj-$(CONFIG_SURFACE_SAM_SID_POWER)	+= surface_sam_sid_power.o
+obj-$(CONFIG_SURFACE_SAM_SID_VHF)	+= surface_sam_sid_vhf.o
+obj-$(CONFIG_SURFACE_SAM_DEBUGFS)	+= surface_sam_debugfs.o
diff --git a/drivers/platform/x86/surface_sam/surface_sam_debugfs.c b/drivers/platform/x86/surface_sam/surface_sam_debugfs.c
new file mode 100644
index 000000000000..13e93404775c
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_debugfs.c
@@ -0,0 +1,270 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/debugfs.h>
+#include <linux/fs.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+
+#include "surface_sam_ssh.h"
+
+#define SSAM_DBGDEV_NAME	"surface_sam_dbgdev"
+#define SSAM_DBGDEV_VERS	0x0100
+
+
+struct ssam_dbgdev_request {
+	__u8 target_category;
+	__u8 command_id;
+	__u8 instance_id;
+	__u8 channel;
+	__u16 flags;
+	__s16 status;
+
+	struct {
+		__u8 __pad[6];
+		__u16 length;
+		const __u8 __user *data;
+	} payload;
+
+	struct {
+		__u8 __pad[6];
+		__u16 length;
+		__u8 __user *data;
+	} response;
+};
+
+#define SSAM_DBGDEV_IOCTL_GETVERSION  _IOR(0xA5, 0, __u32)
+#define SSAM_DBGDEV_IOCTL_REQUEST     _IOWR(0xA5, 1, struct ssam_dbgdev_request)
+
+
+struct ssam_dbgdev {
+	struct ssam_controller *ctrl;
+	struct dentry *dentry_dir;
+	struct dentry *dentry_dev;
+};
+
+
+static int ssam_dbgdev_open(struct inode *inode, struct file *filp)
+{
+	filp->private_data = inode->i_private;
+	return nonseekable_open(inode, filp);
+}
+
+static long ssam_dbgdev_request(struct file *file, unsigned long arg)
+{
+	struct ssam_dbgdev *ddev = file->private_data;
+	struct ssam_dbgdev_request __user *r;
+	struct ssam_dbgdev_request rqst;
+	struct ssam_request spec;
+	struct ssam_response rsp;
+	u8 *pldbuf = NULL;
+	u8 *rspbuf = NULL;
+	int status = 0, ret = 0, tmp;
+
+	r = (struct ssam_dbgdev_request __user *)arg;
+	ret = copy_struct_from_user(&rqst, sizeof(rqst), r, sizeof(*r));
+	if (ret)
+		goto out;
+
+	// setup basic request fields
+	spec.target_category = rqst.target_category;
+	spec.command_id = rqst.command_id;
+	spec.instance_id = rqst.instance_id;
+	spec.channel = rqst.channel;
+	spec.flags = rqst.flags;
+	spec.length = rqst.payload.length;
+
+	rsp.capacity = rqst.response.length;
+	rsp.length = 0;
+
+	// get request payload from user-space
+	if (spec.length) {
+		if (!rqst.payload.data) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		pldbuf = kzalloc(spec.length, GFP_KERNEL);
+		if (!pldbuf) {
+			status = -ENOMEM;
+			ret = -EFAULT;
+			goto out;
+		}
+
+		if (copy_from_user(pldbuf, rqst.payload.data, spec.length)) {
+			ret = -EFAULT;
+			goto out;
+		}
+	}
+	spec.payload = pldbuf;
+
+	// allocate response buffer
+	if (rsp.capacity) {
+		if (!rqst.response.data) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		rspbuf = kzalloc(rsp.capacity, GFP_KERNEL);
+		if (!rspbuf) {
+			status = -ENOMEM;
+			ret = -EFAULT;
+			goto out;
+		}
+	}
+	rsp.pointer = rspbuf;
+
+	// perform request
+	status = ssam_request_sync(ddev->ctrl, &spec, &rsp);
+	if (status)
+		goto out;
+
+	// copy response to user-space
+	if (rsp.length) {
+		if (copy_to_user(rqst.response.data, rsp.pointer, rsp.length)) {
+			ret = -EFAULT;
+			goto out;
+		}
+	}
+
+out:
+	// always try to set response-length and status
+	tmp = put_user(rsp.length, &r->response.length);
+	if (!ret)
+		ret = tmp;
+
+	tmp = put_user(status, &r->status);
+	if (!ret)
+		ret = tmp;
+
+	// cleanup
+	if (pldbuf)
+		kfree(pldbuf);
+
+	if (rspbuf)
+		kfree(rspbuf);
+
+	return ret;
+}
+
+static long ssam_dbgdev_getversion(struct file *file, unsigned long arg)
+{
+	put_user(SSAM_DBGDEV_VERS, (u32 __user *)arg);
+	return 0;
+}
+
+static long ssam_dbgdev_ioctl(struct file *file, unsigned int cmd,
+			      unsigned long arg)
+{
+	switch (cmd) {
+	case SSAM_DBGDEV_IOCTL_GETVERSION:
+		return ssam_dbgdev_getversion(file, arg);
+
+	case SSAM_DBGDEV_IOCTL_REQUEST:
+		return ssam_dbgdev_request(file, arg);
+
+	default:
+		return -EINVAL;
+	}
+}
+
+const struct file_operations ssam_dbgdev_fops = {
+	.owner          = THIS_MODULE,
+	.open           = ssam_dbgdev_open,
+	.unlocked_ioctl = ssam_dbgdev_ioctl,
+	.compat_ioctl   = ssam_dbgdev_ioctl,
+	.llseek         = noop_llseek,
+};
+
+static int ssam_dbgdev_probe(struct platform_device *pdev)
+{
+	struct ssam_dbgdev *ddev;
+	struct ssam_controller *ctrl;
+	int status;
+
+	status = ssam_client_bind(&pdev->dev, &ctrl);
+	if (status)
+		return status == -ENXIO ? -EPROBE_DEFER : status;
+
+	ddev = devm_kzalloc(&pdev->dev, sizeof(struct ssam_dbgdev), GFP_KERNEL);
+	if (!ddev)
+		return -ENOMEM;
+
+	ddev->ctrl = ctrl;
+
+	ddev->dentry_dir = debugfs_create_dir("surface_sam", NULL);
+	if (IS_ERR(ddev->dentry_dir))
+		return PTR_ERR(ddev->dentry_dir);
+
+	ddev->dentry_dev = debugfs_create_file("controller", 0600,
+					       ddev->dentry_dir, ddev,
+					       &ssam_dbgdev_fops);
+	if (IS_ERR(ddev->dentry_dev)) {
+		debugfs_remove(ddev->dentry_dir);
+		return PTR_ERR(ddev->dentry_dev);
+	}
+
+	platform_set_drvdata(pdev, ddev);
+	return 0;
+}
+
+static int ssam_dbgdev_remove(struct platform_device *pdev)
+{
+	struct ssam_dbgdev *ddev = platform_get_drvdata(pdev);
+
+	debugfs_remove(ddev->dentry_dev);
+	debugfs_remove(ddev->dentry_dir);
+
+	platform_set_drvdata(pdev, NULL);
+	return 0;
+}
+
+static void ssam_dbgdev_release(struct device *dev)
+{
+	// nothing to do
+}
+
+
+static struct platform_device ssam_dbgdev_device = {
+	.name = SSAM_DBGDEV_NAME,
+	.id = PLATFORM_DEVID_NONE,
+	.dev.release = ssam_dbgdev_release,
+};
+
+static struct platform_driver ssam_dbgdev_driver = {
+	.probe 	= ssam_dbgdev_probe,
+	.remove = ssam_dbgdev_remove,
+	.driver = {
+		.name = SSAM_DBGDEV_NAME,
+	},
+};
+
+static int __init surface_sam_debugfs_init(void)
+{
+	int status;
+
+	status = platform_device_register(&ssam_dbgdev_device);
+	if (status)
+		return status;
+
+	status = platform_driver_register(&ssam_dbgdev_driver);
+	if (status)
+		platform_device_unregister(&ssam_dbgdev_device);
+
+	return status;
+}
+
+static void __exit surface_sam_debugfs_exit(void)
+{
+	platform_driver_unregister(&ssam_dbgdev_driver);
+	platform_device_unregister(&ssam_dbgdev_device);
+}
+
+module_init(surface_sam_debugfs_init);
+module_exit(surface_sam_debugfs_exit);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("DebugFS entries for Surface Aggregator Module");
+MODULE_LICENSE("GPL");
diff --git a/drivers/platform/x86/surface_sam/surface_sam_dtx.c b/drivers/platform/x86/surface_sam/surface_sam_dtx.c
new file mode 100644
index 000000000000..9c844bb0f773
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_dtx.c
@@ -0,0 +1,582 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Detachment system (DTX) driver for Microsoft Surface Book 2.
+ */
+
+#include <linux/acpi.h>
+#include <linux/delay.h>
+#include <linux/fs.h>
+#include <linux/input.h>
+#include <linux/ioctl.h>
+#include <linux/kernel.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/poll.h>
+#include <linux/rculist.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/platform_device.h>
+
+#include "surface_sam_ssh.h"
+
+
+#define USB_VENDOR_ID_MICROSOFT				0x045e
+#define USB_DEVICE_ID_MS_SURFACE_BASE_2_INTEGRATION	0x0922
+
+// name copied from MS device manager
+#define DTX_INPUT_NAME	"Microsoft Surface Base 2 Integration Device"
+
+
+#define DTX_CMD_LATCH_LOCK				_IO(0x11, 0x01)
+#define DTX_CMD_LATCH_UNLOCK				_IO(0x11, 0x02)
+#define DTX_CMD_LATCH_REQUEST				_IO(0x11, 0x03)
+#define DTX_CMD_LATCH_OPEN				_IO(0x11, 0x04)
+#define DTX_CMD_GET_OPMODE				_IOR(0x11, 0x05, int)
+
+#define SAM_EVENT_DTX_CID_CONNECTION			0x0c
+#define SAM_EVENT_DTX_CID_BUTTON			0x0e
+#define SAM_EVENT_DTX_CID_ERROR				0x0f
+#define SAM_EVENT_DTX_CID_LATCH_STATUS			0x11
+
+#define DTX_OPMODE_TABLET				0x00
+#define DTX_OPMODE_LAPTOP				0x01
+#define DTX_OPMODE_STUDIO				0x02
+
+#define DTX_LATCH_CLOSED				0x00
+#define DTX_LATCH_OPENED				0x01
+
+
+// Warning: This must always be a power of 2!
+#define DTX_CLIENT_BUF_SIZE				16
+
+#define DTX_CONNECT_OPMODE_DELAY			1000
+
+#define DTX_ERR		KERN_ERR "surface_sam_dtx: "
+#define DTX_WARN	KERN_WARNING "surface_sam_dtx: "
+
+
+struct surface_dtx_event {
+	u8 type;
+	u8 code;
+	u8 arg0;
+	u8 arg1;
+} __packed;
+
+struct surface_dtx_dev {
+	struct ssam_controller *ctrl;
+
+	struct ssam_event_notifier notif;
+	struct delayed_work opmode_work;
+	wait_queue_head_t waitq;
+	struct miscdevice mdev;
+	spinlock_t client_lock;
+	struct list_head client_list;
+	struct mutex mutex;
+	bool active;
+	spinlock_t input_lock;
+	struct input_dev *input_dev;
+};
+
+struct surface_dtx_client {
+	struct list_head node;
+	struct surface_dtx_dev *ddev;
+	struct fasync_struct *fasync;
+	spinlock_t buffer_lock;
+	unsigned int buffer_head;
+	unsigned int buffer_tail;
+	struct surface_dtx_event buffer[DTX_CLIENT_BUF_SIZE];
+};
+
+
+static struct surface_dtx_dev surface_dtx_dev;
+
+
+static SSAM_DEFINE_SYNC_REQUEST_N(ssam_bas_latch_lock, {
+	.target_category = SSAM_SSH_TC_BAS,
+	.command_id      = 0x06,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static SSAM_DEFINE_SYNC_REQUEST_N(ssam_bas_latch_unlock, {
+	.target_category = SSAM_SSH_TC_BAS,
+	.command_id      = 0x07,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static SSAM_DEFINE_SYNC_REQUEST_N(ssam_bas_latch_request, {
+	.target_category = SSAM_SSH_TC_BAS,
+	.command_id      = 0x08,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static SSAM_DEFINE_SYNC_REQUEST_N(ssam_bas_latch_open, {
+	.target_category = SSAM_SSH_TC_BAS,
+	.command_id      = 0x09,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static SSAM_DEFINE_SYNC_REQUEST_R(ssam_bas_query_opmode, u8, {
+	.target_category = SSAM_SSH_TC_BAS,
+	.command_id      = 0x0d,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+
+static int dtx_bas_get_opmode(struct ssam_controller *ctrl, int __user *buf)
+{
+	u8 opmode;
+	int status;
+
+	status = ssam_bas_query_opmode(ctrl, &opmode);
+	if (status < 0)
+		return status;
+
+	if (put_user(opmode, buf))
+		return -EACCES;
+
+	return 0;
+}
+
+
+static int surface_dtx_open(struct inode *inode, struct file *file)
+{
+	struct surface_dtx_dev *ddev = container_of(file->private_data, struct surface_dtx_dev, mdev);
+	struct surface_dtx_client *client;
+
+	// initialize client
+	client = kzalloc(sizeof(struct surface_dtx_client), GFP_KERNEL);
+	if (!client)
+		return -ENOMEM;
+
+	spin_lock_init(&client->buffer_lock);
+	client->buffer_head = 0;
+	client->buffer_tail = 0;
+	client->ddev = ddev;
+
+	// attach client
+	spin_lock(&ddev->client_lock);
+	list_add_tail_rcu(&client->node, &ddev->client_list);
+	spin_unlock(&ddev->client_lock);
+
+	file->private_data = client;
+	nonseekable_open(inode, file);
+
+	return 0;
+}
+
+static int surface_dtx_release(struct inode *inode, struct file *file)
+{
+	struct surface_dtx_client *client = file->private_data;
+
+	// detach client
+	spin_lock(&client->ddev->client_lock);
+	list_del_rcu(&client->node);
+	spin_unlock(&client->ddev->client_lock);
+	synchronize_rcu();
+
+	kfree(client);
+	file->private_data = NULL;
+
+	return 0;
+}
+
+static ssize_t surface_dtx_read(struct file *file, char __user *buf, size_t count, loff_t *offs)
+{
+	struct surface_dtx_client *client = file->private_data;
+	struct surface_dtx_dev *ddev = client->ddev;
+	struct surface_dtx_event event;
+	size_t read = 0;
+	int status = 0;
+
+	if (count != 0 && count < sizeof(struct surface_dtx_event))
+		return -EINVAL;
+
+	if (!ddev->active)
+		return -ENODEV;
+
+	// check availability
+	if (client->buffer_head == client->buffer_tail) {
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+
+		status = wait_event_interruptible(ddev->waitq,
+				client->buffer_head != client->buffer_tail ||
+				!ddev->active);
+		if (status)
+			return status;
+
+		if (!ddev->active)
+			return -ENODEV;
+	}
+
+	// copy events one by one
+	while (read + sizeof(struct surface_dtx_event) <= count) {
+		spin_lock_irq(&client->buffer_lock);
+
+		if (client->buffer_head == client->buffer_tail) {
+			spin_unlock_irq(&client->buffer_lock);
+			break;
+		}
+
+		// get one event
+		event = client->buffer[client->buffer_tail];
+		client->buffer_tail = (client->buffer_tail + 1) & (DTX_CLIENT_BUF_SIZE - 1);
+		spin_unlock_irq(&client->buffer_lock);
+
+		// copy to userspace
+		if (copy_to_user(buf, &event, sizeof(struct surface_dtx_event)))
+			return -EFAULT;
+
+		read += sizeof(struct surface_dtx_event);
+	}
+
+	return read;
+}
+
+static __poll_t surface_dtx_poll(struct file *file, struct poll_table_struct *pt)
+{
+	struct surface_dtx_client *client = file->private_data;
+	int mask;
+
+	poll_wait(file, &client->ddev->waitq, pt);
+
+	if (client->ddev->active)
+		mask = EPOLLOUT | EPOLLWRNORM;
+	else
+		mask = EPOLLHUP | EPOLLERR;
+
+	if (client->buffer_head != client->buffer_tail)
+		mask |= EPOLLIN | EPOLLRDNORM;
+
+	return mask;
+}
+
+static int surface_dtx_fasync(int fd, struct file *file, int on)
+{
+	struct surface_dtx_client *client = file->private_data;
+
+	return fasync_helper(fd, file, on, &client->fasync);
+}
+
+static long surface_dtx_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	struct surface_dtx_client *client = file->private_data;
+	struct surface_dtx_dev *ddev = client->ddev;
+	int status;
+
+	status = mutex_lock_interruptible(&ddev->mutex);
+	if (status)
+		return status;
+
+	if (!ddev->active) {
+		mutex_unlock(&ddev->mutex);
+		return -ENODEV;
+	}
+
+	switch (cmd) {
+	case DTX_CMD_LATCH_LOCK:
+		status = ssam_bas_latch_lock(ddev->ctrl);
+		break;
+
+	case DTX_CMD_LATCH_UNLOCK:
+		status = ssam_bas_latch_unlock(ddev->ctrl);
+		break;
+
+	case DTX_CMD_LATCH_REQUEST:
+		status = ssam_bas_latch_request(ddev->ctrl);
+		break;
+
+	case DTX_CMD_LATCH_OPEN:
+		status = ssam_bas_latch_open(ddev->ctrl);
+		break;
+
+	case DTX_CMD_GET_OPMODE:
+		status = dtx_bas_get_opmode(ddev->ctrl, (int __user *)arg);
+		break;
+
+	default:
+		status = -EINVAL;
+		break;
+	}
+
+	mutex_unlock(&ddev->mutex);
+	return status;
+}
+
+static const struct file_operations surface_dtx_fops = {
+	.owner          = THIS_MODULE,
+	.open           = surface_dtx_open,
+	.release        = surface_dtx_release,
+	.read           = surface_dtx_read,
+	.poll           = surface_dtx_poll,
+	.fasync         = surface_dtx_fasync,
+	.unlocked_ioctl = surface_dtx_ioctl,
+	.llseek         = no_llseek,
+};
+
+static struct surface_dtx_dev surface_dtx_dev = {
+	.mdev = {
+		.minor = MISC_DYNAMIC_MINOR,
+		.name = "surface_dtx",
+		.fops = &surface_dtx_fops,
+	},
+	.client_lock = __SPIN_LOCK_UNLOCKED(),
+	.input_lock = __SPIN_LOCK_UNLOCKED(),
+	.mutex  = __MUTEX_INITIALIZER(surface_dtx_dev.mutex),
+	.active = false,
+};
+
+
+static void surface_dtx_push_event(struct surface_dtx_dev *ddev, struct surface_dtx_event *event)
+{
+	struct surface_dtx_client *client;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(client, &ddev->client_list, node) {
+		spin_lock(&client->buffer_lock);
+
+		client->buffer[client->buffer_head++] = *event;
+		client->buffer_head &= DTX_CLIENT_BUF_SIZE - 1;
+
+		if (unlikely(client->buffer_head == client->buffer_tail)) {
+			printk(DTX_WARN "event buffer overrun\n");
+			client->buffer_tail = (client->buffer_tail + 1) & (DTX_CLIENT_BUF_SIZE - 1);
+		}
+
+		spin_unlock(&client->buffer_lock);
+
+		kill_fasync(&client->fasync, SIGIO, POLL_IN);
+	}
+	rcu_read_unlock();
+
+	wake_up_interruptible(&ddev->waitq);
+}
+
+
+static void surface_dtx_update_opmpde(struct surface_dtx_dev *ddev)
+{
+	struct surface_dtx_event event;
+	u8 opmode;
+	int status;
+
+	// get operation mode
+	status = ssam_bas_query_opmode(ddev->ctrl, &opmode);
+	if (status < 0) {
+		printk(DTX_ERR "EC request failed with error %d\n", status);
+		return;
+	}
+
+	// send DTX event
+	event.type = 0x11;
+	event.code = 0x0D;
+	event.arg0 = opmode;
+	event.arg1 = 0x00;
+
+	surface_dtx_push_event(ddev, &event);
+
+	// send SW_TABLET_MODE event
+	spin_lock(&ddev->input_lock);
+	input_report_switch(ddev->input_dev, SW_TABLET_MODE, opmode != DTX_OPMODE_LAPTOP);
+	input_sync(ddev->input_dev);
+	spin_unlock(&ddev->input_lock);
+}
+
+static void surface_dtx_opmode_workfn(struct work_struct *work)
+{
+	struct surface_dtx_dev *ddev = container_of(work, struct surface_dtx_dev, opmode_work.work);
+
+	surface_dtx_update_opmpde(ddev);
+}
+
+static u32 surface_dtx_notification(struct ssam_notifier_block *nb, const struct ssam_event *in_event)
+{
+	struct surface_dtx_dev *ddev = container_of(nb, struct surface_dtx_dev, notif.base);
+	struct surface_dtx_event event;
+	unsigned long delay;
+
+	switch (in_event->command_id) {
+	case SAM_EVENT_DTX_CID_CONNECTION:
+	case SAM_EVENT_DTX_CID_BUTTON:
+	case SAM_EVENT_DTX_CID_ERROR:
+	case SAM_EVENT_DTX_CID_LATCH_STATUS:
+		if (in_event->length > 2) {
+			printk(DTX_ERR "unexpected payload size (cid: %x, len: %u)\n",
+			       in_event->command_id, in_event->length);
+			return SSAM_NOTIF_HANDLED;
+		}
+
+		event.type = in_event->target_category;
+		event.code = in_event->command_id;
+		event.arg0 = in_event->length >= 1 ? in_event->data[0] : 0x00;
+		event.arg1 = in_event->length >= 2 ? in_event->data[1] : 0x00;
+		surface_dtx_push_event(ddev, &event);
+		break;
+
+	default:
+		return 0;
+	}
+
+	// update device mode
+	if (in_event->command_id == SAM_EVENT_DTX_CID_CONNECTION) {
+		delay = event.arg0 ? DTX_CONNECT_OPMODE_DELAY : 0;
+		schedule_delayed_work(&ddev->opmode_work, delay);
+	}
+
+	return SSAM_NOTIF_HANDLED;
+}
+
+
+static struct input_dev *surface_dtx_register_inputdev(
+		struct platform_device *pdev, struct ssam_controller *ctrl)
+{
+	struct input_dev *input_dev;
+	u8 opmode;
+	int status;
+
+	input_dev = input_allocate_device();
+	if (!input_dev)
+		return ERR_PTR(-ENOMEM);
+
+	input_dev->name = DTX_INPUT_NAME;
+	input_dev->dev.parent = &pdev->dev;
+	input_dev->id.bustype = BUS_VIRTUAL;
+	input_dev->id.vendor  = USB_VENDOR_ID_MICROSOFT;
+	input_dev->id.product = USB_DEVICE_ID_MS_SURFACE_BASE_2_INTEGRATION;
+
+	input_set_capability(input_dev, EV_SW, SW_TABLET_MODE);
+
+	status = ssam_bas_query_opmode(ctrl, &opmode);
+	if (status < 0) {
+		input_free_device(input_dev);
+		return ERR_PTR(status);
+	}
+
+	input_report_switch(input_dev, SW_TABLET_MODE, opmode != DTX_OPMODE_LAPTOP);
+
+	status = input_register_device(input_dev);
+	if (status) {
+		input_unregister_device(input_dev);
+		return ERR_PTR(status);
+	}
+
+	return input_dev;
+}
+
+
+static int surface_sam_dtx_probe(struct platform_device *pdev)
+{
+	struct surface_dtx_dev *ddev = &surface_dtx_dev;
+	struct ssam_controller *ctrl;
+	struct input_dev *input_dev;
+	int status;
+
+	// link to ec
+	status = ssam_client_bind(&pdev->dev, &ctrl);
+	if (status)
+		return status == -ENXIO ? -EPROBE_DEFER : status;
+
+	input_dev = surface_dtx_register_inputdev(pdev, ctrl);
+	if (IS_ERR(input_dev))
+		return PTR_ERR(input_dev);
+
+	// initialize device
+	mutex_lock(&ddev->mutex);
+	if (ddev->active) {
+		mutex_unlock(&ddev->mutex);
+		status = -ENODEV;
+		goto err_register;
+	}
+
+	ddev->ctrl = ctrl;
+	INIT_DELAYED_WORK(&ddev->opmode_work, surface_dtx_opmode_workfn);
+	INIT_LIST_HEAD(&ddev->client_list);
+	init_waitqueue_head(&ddev->waitq);
+	ddev->active = true;
+	ddev->input_dev = input_dev;
+	mutex_unlock(&ddev->mutex);
+
+	status = misc_register(&ddev->mdev);
+	if (status)
+		goto err_register;
+
+	// set up events
+	ddev->notif.base.priority = 1;
+	ddev->notif.base.fn = surface_dtx_notification;
+	ddev->notif.event.reg = SSAM_EVENT_REGISTRY_SAM;
+	ddev->notif.event.id.target_category = SSAM_SSH_TC_BAS;
+	ddev->notif.event.id.instance = 0;
+	ddev->notif.event.flags = SSAM_EVENT_SEQUENCED;
+
+	status = ssam_notifier_register(ctrl, &ddev->notif);
+	if (status)
+		goto err_events_setup;
+
+	return 0;
+
+err_events_setup:
+	misc_deregister(&ddev->mdev);
+err_register:
+	input_unregister_device(ddev->input_dev);
+	return status;
+}
+
+static int surface_sam_dtx_remove(struct platform_device *pdev)
+{
+	struct surface_dtx_dev *ddev = &surface_dtx_dev;
+	struct surface_dtx_client *client;
+
+	mutex_lock(&ddev->mutex);
+	if (!ddev->active) {
+		mutex_unlock(&ddev->mutex);
+		return 0;
+	}
+
+	// mark as inactive
+	ddev->active = false;
+	mutex_unlock(&ddev->mutex);
+
+	// After this call we're guaranteed that no more input events will arive
+	ssam_notifier_unregister(ddev->ctrl, &ddev->notif);
+
+	// wake up clients
+	spin_lock(&ddev->client_lock);
+	list_for_each_entry(client, &ddev->client_list, node) {
+		kill_fasync(&client->fasync, SIGIO, POLL_HUP);
+	}
+	spin_unlock(&ddev->client_lock);
+
+	wake_up_interruptible(&ddev->waitq);
+
+	// unregister user-space devices
+	input_unregister_device(ddev->input_dev);
+	misc_deregister(&ddev->mdev);
+
+	return 0;
+}
+
+
+static const struct acpi_device_id surface_sam_dtx_match[] = {
+	{ "MSHW0133", 0 },
+	{ },
+};
+MODULE_DEVICE_TABLE(acpi, surface_sam_dtx_match);
+
+static struct platform_driver surface_sam_dtx = {
+	.probe = surface_sam_dtx_probe,
+	.remove = surface_sam_dtx_remove,
+	.driver = {
+		.name = "surface_sam_dtx",
+		.acpi_match_table = surface_sam_dtx_match,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+module_platform_driver(surface_sam_dtx);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("Surface Detachment System (DTX) Driver for 5th Generation Surface Devices");
+MODULE_LICENSE("GPL");
diff --git a/drivers/platform/x86/surface_sam/surface_sam_hps.c b/drivers/platform/x86/surface_sam/surface_sam_hps.c
new file mode 100644
index 000000000000..b11f9fa8095f
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_hps.c
@@ -0,0 +1,1287 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Surface dGPU hot-plug system driver.
+ * Supports explicit setting of the dGPU power-state on the Surface Book 2 and
+ * properly handles hot-plugging by detaching the base.
+ */
+
+#include <linux/acpi.h>
+#include <linux/delay.h>
+#include <linux/gpio.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/pci.h>
+#include <linux/platform_device.h>
+#include <linux/sysfs.h>
+
+#include "surface_sam_ssh.h"
+#include "surface_sam_san.h"
+
+
+// TODO: vgaswitcheroo integration
+
+
+static void dbg_dump_drvsta(struct platform_device *pdev, const char *prefix);
+
+
+#define SHPS_DSM_REVISION	1
+#define SHPS_DSM_GPU_ADDRS	0x02
+#define SHPS_DSM_GPU_POWER	0x05
+static const guid_t SHPS_DSM_UUID =
+	GUID_INIT(0x5515a847, 0xed55, 0x4b27, 0x83, 0x52, 0xcd,
+		  0x32, 0x0e, 0x10, 0x36, 0x0a);
+
+
+#define SAM_DGPU_TC			0x13
+#define SAM_DGPU_CID_POWERON		0x02
+#define ACPI_SGCP_NOTIFY_POWER_ON	0x81
+
+#define SHPS_DSM_GPU_ADDRS_RP		"RP5_PCIE"
+#define SHPS_DSM_GPU_ADDRS_DGPU		"DGPU_PCIE"
+#define SHPS_PCI_GPU_ADDR_RP			"\\_SB.PCI0.RP13._ADR"
+
+static const struct acpi_gpio_params gpio_base_presence_int = { 0, 0, false };
+static const struct acpi_gpio_params gpio_base_presence     = { 1, 0, false };
+static const struct acpi_gpio_params gpio_dgpu_power_int    = { 2, 0, false };
+static const struct acpi_gpio_params gpio_dgpu_power        = { 3, 0, false };
+static const struct acpi_gpio_params gpio_dgpu_presence_int = { 4, 0, false };
+static const struct acpi_gpio_params gpio_dgpu_presence     = { 5, 0, false };
+
+static const struct acpi_gpio_mapping shps_acpi_gpios[] = {
+	{ "base_presence-int-gpio", &gpio_base_presence_int, 1 },
+	{ "base_presence-gpio",     &gpio_base_presence,     1 },
+	{ "dgpu_power-int-gpio",    &gpio_dgpu_power_int,    1 },
+	{ "dgpu_power-gpio",        &gpio_dgpu_power,        1 },
+	{ "dgpu_presence-int-gpio", &gpio_dgpu_presence_int, 1 },
+	{ "dgpu_presence-gpio",     &gpio_dgpu_presence,     1 },
+	{ },
+};
+
+
+enum shps_dgpu_power {
+	SHPS_DGPU_POWER_OFF      = 0,
+	SHPS_DGPU_POWER_ON       = 1,
+	SHPS_DGPU_POWER_UNKNOWN  = 2,
+};
+
+static const char *shps_dgpu_power_str(enum shps_dgpu_power power)
+{
+	if (power == SHPS_DGPU_POWER_OFF)
+		return "off";
+	else if (power == SHPS_DGPU_POWER_ON)
+		return "on";
+	else if (power == SHPS_DGPU_POWER_UNKNOWN)
+		return "unknown";
+	else
+		return "<invalid>";
+}
+
+enum shps_notification_method {
+	SHPS_NOTIFICATION_METHOD_SAN = 1,
+	SHPS_NOTIFICATION_METHOD_SGCP = 2
+};
+
+struct shps_hardware_traits {
+	enum shps_notification_method notification_method;
+	const char *dgpu_rp_pci_address;
+};
+
+struct shps_driver_data {
+	struct ssam_controller *ctrl;
+
+	struct mutex lock;
+	struct pci_dev *dgpu_root_port;
+	struct pci_saved_state *dgpu_root_port_state;
+	struct gpio_desc *gpio_dgpu_power;
+	struct gpio_desc *gpio_dgpu_presence;
+	struct gpio_desc *gpio_base_presence;
+	unsigned int irq_dgpu_presence;
+	unsigned int irq_base_presence;
+	unsigned long state;
+	acpi_handle sgpc_handle;
+	struct shps_hardware_traits hardware_traits;
+};
+
+struct shps_hardware_probe {
+	const char *hardware_id;
+	int generation;
+	struct shps_hardware_traits *hardware_traits;
+};
+
+static struct shps_hardware_traits shps_gen1_hwtraits = {
+	.notification_method = SHPS_NOTIFICATION_METHOD_SAN
+};
+
+static struct shps_hardware_traits shps_gen2_hwtraits = {
+	.notification_method = SHPS_NOTIFICATION_METHOD_SGCP,
+	.dgpu_rp_pci_address = SHPS_PCI_GPU_ADDR_RP
+};
+
+static const struct shps_hardware_probe shps_hardware_probe_match[] = {
+	/* Surface Book 3 */
+	{ "MSHW0117", 2, &shps_gen2_hwtraits },
+
+	/* Surface Book 2 (default, must be last entry) */
+	{ NULL, 1, &shps_gen1_hwtraits }
+};
+
+#define SHPS_STATE_BIT_PWRTGT		0	/* desired power state: 1 for on, 0 for off */
+#define SHPS_STATE_BIT_RPPWRON_SYNC	1	/* synchronous/requested power-up in progress  */
+#define SHPS_STATE_BIT_WAKE_ENABLED	2	/* wakeup via base-presence GPIO enabled */
+
+
+#define SHPS_DGPU_PARAM_PERM		0644
+
+enum shps_dgpu_power_mp {
+	SHPS_DGPU_MP_POWER_OFF  = SHPS_DGPU_POWER_OFF,
+	SHPS_DGPU_MP_POWER_ON   = SHPS_DGPU_POWER_ON,
+	SHPS_DGPU_MP_POWER_ASIS = -1,
+
+	__SHPS_DGPU_MP_POWER_START = -1,
+	__SHPS_DGPU_MP_POWER_END   = 1,
+};
+
+static int param_dgpu_power_set(const char *val, const struct kernel_param *kp)
+{
+	int power = SHPS_DGPU_MP_POWER_OFF;
+	int status;
+
+	status = kstrtoint(val, 0, &power);
+	if (status)
+		return status;
+
+	if (power < __SHPS_DGPU_MP_POWER_START || power > __SHPS_DGPU_MP_POWER_END)
+		return -EINVAL;
+
+	return param_set_int(val, kp);
+}
+
+static const struct kernel_param_ops param_dgpu_power_ops = {
+	.set = param_dgpu_power_set,
+	.get = param_get_int,
+};
+
+static int param_dgpu_power_init = SHPS_DGPU_MP_POWER_OFF;
+static int param_dgpu_power_exit = SHPS_DGPU_MP_POWER_ON;
+static int param_dgpu_power_susp = SHPS_DGPU_MP_POWER_ASIS;
+static bool param_dtx_latch = true;
+
+module_param_cb(dgpu_power_init, &param_dgpu_power_ops, &param_dgpu_power_init, SHPS_DGPU_PARAM_PERM);
+module_param_cb(dgpu_power_exit, &param_dgpu_power_ops, &param_dgpu_power_exit, SHPS_DGPU_PARAM_PERM);
+module_param_cb(dgpu_power_susp, &param_dgpu_power_ops, &param_dgpu_power_susp, SHPS_DGPU_PARAM_PERM);
+module_param_named(dtx_latch, param_dtx_latch, bool, SHPS_DGPU_PARAM_PERM);
+
+MODULE_PARM_DESC(dgpu_power_init, "dGPU power state to be set on init (0: off / 1: on / 2: as-is, default: off)");
+MODULE_PARM_DESC(dgpu_power_exit, "dGPU power state to be set on exit (0: off / 1: on / 2: as-is, default: on)");
+MODULE_PARM_DESC(dgpu_power_susp, "dGPU power state to be set on exit (0: off / 1: on / 2: as-is, default: as-is)");
+MODULE_PARM_DESC(dtx_latch, "lock/unlock DTX base latch in accordance to power-state (Y/n)");
+
+static SSAM_DEFINE_SYNC_REQUEST_N(ssam_bas_latch_lock, {
+	.target_category = SSAM_SSH_TC_BAS,
+	.command_id      = 0x06,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static SSAM_DEFINE_SYNC_REQUEST_N(ssam_bas_latch_unlock, {
+	.target_category = SSAM_SSH_TC_BAS,
+	.command_id      = 0x07,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static int shps_dgpu_dsm_get_pci_addr_from_adr(struct platform_device *pdev, const char *entry) {
+	acpi_handle handle = ACPI_HANDLE(&pdev->dev);
+	int status;
+	struct acpi_object_list input;
+	union acpi_object input_args[0];
+	u64 device_addr;
+	u8 bus, dev, fun;
+
+	input.count = 0;
+	input.pointer = input_args;
+
+
+	status = acpi_evaluate_integer(handle, (acpi_string)entry, &input, &device_addr);
+	if (status) {
+		return -ENODEV;
+	}
+
+	bus = 0;
+	dev = (device_addr & 0xFF0000) >> 16;
+	fun = device_addr & 0xFF;
+
+	dev_info(&pdev->dev, "found pci device at bus = %d, dev = %x, fun = %x\n",
+		 (u32)bus, (u32)dev, (u32)fun);
+
+	return bus << 8 | PCI_DEVFN(dev, fun);
+}
+
+static int shps_dgpu_dsm_get_pci_addr_from_dsm(struct platform_device *pdev, const char *entry)
+{
+	acpi_handle handle = ACPI_HANDLE(&pdev->dev);
+	union acpi_object *result;
+	union acpi_object *e0;
+	union acpi_object *e1;
+	union acpi_object *e2;
+	u64 device_addr = 0;
+	u8 bus, dev, fun;
+	int i;
+
+
+	result = acpi_evaluate_dsm_typed(handle, &SHPS_DSM_UUID, SHPS_DSM_REVISION,
+					 SHPS_DSM_GPU_ADDRS, NULL, ACPI_TYPE_PACKAGE);
+
+	if (IS_ERR_OR_NULL(result))
+		return result ? PTR_ERR(result) : -EIO;
+
+	// three entries per device: name, address, <integer>
+	for (i = 0; i + 2 < result->package.count; i += 3) {
+		e0 = &result->package.elements[i];
+		e1 = &result->package.elements[i + 1];
+		e2 = &result->package.elements[i + 2];
+
+		if (e0->type != ACPI_TYPE_STRING) {
+			ACPI_FREE(result);
+			return -EIO;
+		}
+
+		if (e1->type != ACPI_TYPE_INTEGER) {
+			ACPI_FREE(result);
+			return -EIO;
+		}
+
+		if (e2->type != ACPI_TYPE_INTEGER) {
+			ACPI_FREE(result);
+			return -EIO;
+		}
+
+		if (strncmp(e0->string.pointer, entry, 64) == 0)
+			device_addr = e1->integer.value;
+	}
+
+	ACPI_FREE(result);
+	if (device_addr == 0)
+		return -ENODEV;
+
+
+	// convert address
+	bus = (device_addr & 0x0FF00000) >> 20;
+	dev = (device_addr & 0x000F8000) >> 15;
+	fun = (device_addr & 0x00007000) >> 12;
+
+	return bus << 8 | PCI_DEVFN(dev, fun);
+}
+
+static struct pci_dev *shps_dgpu_dsm_get_pci_dev(struct platform_device *pdev)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	struct pci_dev *dev;
+	int addr;
+
+
+	if (drvdata->hardware_traits.dgpu_rp_pci_address) {
+		addr = shps_dgpu_dsm_get_pci_addr_from_adr(pdev, drvdata->hardware_traits.dgpu_rp_pci_address);
+	} else {
+		addr = shps_dgpu_dsm_get_pci_addr_from_dsm(pdev, SHPS_DSM_GPU_ADDRS_RP);
+	}
+
+	if (addr < 0)
+		return ERR_PTR(addr);
+
+	dev = pci_get_domain_bus_and_slot(0, (addr & 0xFF00) >> 8, addr & 0xFF);
+	return dev ? dev : ERR_PTR(-ENODEV);
+}
+
+
+static int shps_dgpu_dsm_get_power_unlocked(struct platform_device *pdev)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	struct gpio_desc *gpio = drvdata->gpio_dgpu_power;
+	int status;
+
+	status = gpiod_get_value_cansleep(gpio);
+	if (status < 0)
+		return status;
+
+	return status == 0 ? SHPS_DGPU_POWER_OFF : SHPS_DGPU_POWER_ON;
+}
+
+static int shps_dgpu_dsm_get_power(struct platform_device *pdev)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	int status;
+
+	mutex_lock(&drvdata->lock);
+	status = shps_dgpu_dsm_get_power_unlocked(pdev);
+	mutex_unlock(&drvdata->lock);
+
+	return status;
+}
+
+static int __shps_dgpu_dsm_set_power_unlocked(struct platform_device *pdev, enum shps_dgpu_power power)
+{
+	acpi_handle handle = ACPI_HANDLE(&pdev->dev);
+	union acpi_object *result;
+	union acpi_object param;
+
+	dev_info(&pdev->dev, "setting dGPU direct power to \'%s\'\n", shps_dgpu_power_str(power));
+
+	param.type = ACPI_TYPE_INTEGER;
+	param.integer.value = power == SHPS_DGPU_POWER_ON;
+
+	result = acpi_evaluate_dsm_typed(handle, &SHPS_DSM_UUID, SHPS_DSM_REVISION,
+					 SHPS_DSM_GPU_POWER, &param, ACPI_TYPE_BUFFER);
+
+	if (IS_ERR_OR_NULL(result))
+		return result ? PTR_ERR(result) : -EIO;
+
+	// check for the expected result
+	if (result->buffer.length != 1 || result->buffer.pointer[0] != 0) {
+		ACPI_FREE(result);
+		return -EIO;
+	}
+
+	ACPI_FREE(result);
+	return 0;
+}
+
+static int shps_dgpu_dsm_set_power_unlocked(struct platform_device *pdev, enum shps_dgpu_power power)
+{
+	int status;
+
+	if (power != SHPS_DGPU_POWER_ON && power != SHPS_DGPU_POWER_OFF)
+		return -EINVAL;
+
+	status = shps_dgpu_dsm_get_power_unlocked(pdev);
+	if (status < 0)
+		return status;
+	if (status == power)
+		return 0;
+
+	return __shps_dgpu_dsm_set_power_unlocked(pdev, power);
+}
+
+static int shps_dgpu_dsm_set_power(struct platform_device *pdev, enum shps_dgpu_power power)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	int status;
+
+	mutex_lock(&drvdata->lock);
+	status = shps_dgpu_dsm_set_power_unlocked(pdev, power);
+	mutex_unlock(&drvdata->lock);
+
+	return status;
+}
+
+
+static bool shps_rp_link_up(struct pci_dev *rp)
+{
+	u16 lnksta = 0, sltsta = 0;
+
+	pcie_capability_read_word(rp, PCI_EXP_LNKSTA, &lnksta);
+	pcie_capability_read_word(rp, PCI_EXP_SLTSTA, &sltsta);
+
+	return (lnksta & PCI_EXP_LNKSTA_DLLLA) || (sltsta & PCI_EXP_SLTSTA_PDS);
+}
+
+
+static int shps_dgpu_rp_get_power_unlocked(struct platform_device *pdev)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	struct pci_dev *rp = drvdata->dgpu_root_port;
+
+	if (rp->current_state == PCI_D3hot || rp->current_state == PCI_D3cold)
+		return SHPS_DGPU_POWER_OFF;
+	else if (rp->current_state == PCI_UNKNOWN || rp->current_state == PCI_POWER_ERROR)
+		return SHPS_DGPU_POWER_UNKNOWN;
+	else
+		return SHPS_DGPU_POWER_ON;
+}
+
+static int shps_dgpu_rp_get_power(struct platform_device *pdev)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	int status;
+
+	mutex_lock(&drvdata->lock);
+	status = shps_dgpu_rp_get_power_unlocked(pdev);
+	mutex_unlock(&drvdata->lock);
+
+	return status;
+}
+
+static int __shps_dgpu_rp_set_power_unlocked(struct platform_device *pdev, enum shps_dgpu_power power)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	struct pci_dev *rp = drvdata->dgpu_root_port;
+	int status, i;
+
+	dev_info(&pdev->dev, "setting dGPU power state to \'%s\'\n", shps_dgpu_power_str(power));
+
+	dbg_dump_drvsta(pdev, "__shps_dgpu_rp_set_power_unlocked.1");
+	if (power == SHPS_DGPU_POWER_ON) {
+		set_bit(SHPS_STATE_BIT_RPPWRON_SYNC, &drvdata->state);
+		pci_set_power_state(rp, PCI_D0);
+
+		if (drvdata->dgpu_root_port_state)
+			pci_load_and_free_saved_state(rp, &drvdata->dgpu_root_port_state);
+
+		pci_restore_state(rp);
+
+		if (!pci_is_enabled(rp))
+			pci_enable_device(rp);
+
+		pci_set_master(rp);
+		clear_bit(SHPS_STATE_BIT_RPPWRON_SYNC, &drvdata->state);
+
+		set_bit(SHPS_STATE_BIT_PWRTGT, &drvdata->state);
+	} else {
+		if (!drvdata->dgpu_root_port_state) {
+			pci_save_state(rp);
+			drvdata->dgpu_root_port_state = pci_store_saved_state(rp);
+		}
+
+		/*
+		 * To properly update the hot-plug system we need to "remove" the dGPU
+		 * before disabling it and sending it to D3cold. Following this, we
+		 * need to wait for the link and slot status to actually change.
+		 */
+		status = shps_dgpu_dsm_set_power_unlocked(pdev, SHPS_DGPU_POWER_OFF);
+		if (status)
+			return status;
+
+		for (i = 0; i < 20 && shps_rp_link_up(rp); i++)
+			msleep(50);
+
+		if (shps_rp_link_up(rp))
+			dev_err(&pdev->dev, "dGPU removal via DSM timed out\n");
+
+		pci_clear_master(rp);
+
+		if (pci_is_enabled(rp))
+			pci_disable_device(rp);
+
+		pci_set_power_state(rp, PCI_D3cold);
+
+		clear_bit(SHPS_STATE_BIT_PWRTGT, &drvdata->state);
+	}
+	dbg_dump_drvsta(pdev, "__shps_dgpu_rp_set_power_unlocked.2");
+
+	return 0;
+}
+
+static int shps_dgpu_rp_set_power_unlocked(struct platform_device *pdev, enum shps_dgpu_power power)
+{
+	int status;
+
+	if (power != SHPS_DGPU_POWER_ON && power != SHPS_DGPU_POWER_OFF)
+		return -EINVAL;
+
+	status = shps_dgpu_rp_get_power_unlocked(pdev);
+	if (status < 0)
+		return status;
+	if (status == power)
+		return 0;
+
+	return __shps_dgpu_rp_set_power_unlocked(pdev, power);
+}
+
+static int shps_dgpu_rp_set_power(struct platform_device *pdev, enum shps_dgpu_power power)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	int status;
+
+	mutex_lock(&drvdata->lock);
+	status = shps_dgpu_rp_set_power_unlocked(pdev, power);
+	mutex_unlock(&drvdata->lock);
+
+	return status;
+}
+
+
+static int shps_dgpu_set_power(struct platform_device *pdev, enum shps_dgpu_power power)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	int status;
+
+	if (!param_dtx_latch)
+		return shps_dgpu_rp_set_power(pdev, power);
+
+	if (power == SHPS_DGPU_POWER_ON) {
+		status = ssam_bas_latch_lock(drvdata->ctrl);
+		if (status)
+			return status;
+
+		status = shps_dgpu_rp_set_power(pdev, power);
+		if (status)
+			ssam_bas_latch_unlock(drvdata->ctrl);
+
+	} else {
+		status = shps_dgpu_rp_set_power(pdev, power);
+		if (status)
+			return status;
+
+		status = ssam_bas_latch_unlock(drvdata->ctrl);
+	}
+
+	return status;
+}
+
+
+static int shps_dgpu_is_present(struct platform_device *pdev)
+{
+	struct shps_driver_data *drvdata;
+
+	drvdata = platform_get_drvdata(pdev);
+	return gpiod_get_value_cansleep(drvdata->gpio_dgpu_presence);
+}
+
+
+static ssize_t dgpu_power_show(struct device *dev, struct device_attribute *attr, char *data)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	int power = shps_dgpu_rp_get_power(pdev);
+
+	if (power < 0)
+		return power;
+
+	return sprintf(data, "%s\n", shps_dgpu_power_str(power));
+}
+
+static ssize_t dgpu_power_store(struct device *dev, struct device_attribute *attr,
+				const char *data, size_t count)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	enum shps_dgpu_power power;
+	bool b = false;
+	int status;
+
+	status = kstrtobool(data, &b);
+	if (status)
+		return status;
+
+	status = shps_dgpu_is_present(pdev);
+	if (status <= 0)
+		return status < 0 ? status : -EPERM;
+
+	power = b ? SHPS_DGPU_POWER_ON : SHPS_DGPU_POWER_OFF;
+	status = shps_dgpu_set_power(pdev, power);
+
+	return status < 0 ? status : count;
+}
+
+static ssize_t dgpu_power_dsm_show(struct device *dev, struct device_attribute *attr, char *data)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	int power = shps_dgpu_dsm_get_power(pdev);
+
+	if (power < 0)
+		return power;
+
+	return sprintf(data, "%s\n", shps_dgpu_power_str(power));
+}
+
+static ssize_t dgpu_power_dsm_store(struct device *dev, struct device_attribute *attr,
+				    const char *data, size_t count)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	enum shps_dgpu_power power;
+	bool b = false;
+	int status;
+
+	status = kstrtobool(data, &b);
+	if (status)
+		return status;
+
+	status = shps_dgpu_is_present(pdev);
+	if (status <= 0)
+		return status < 0 ? status : -EPERM;
+
+	power = b ? SHPS_DGPU_POWER_ON : SHPS_DGPU_POWER_OFF;
+	status = shps_dgpu_dsm_set_power(pdev, power);
+
+	return status < 0 ? status : count;
+}
+
+static DEVICE_ATTR_RW(dgpu_power);
+static DEVICE_ATTR_RW(dgpu_power_dsm);
+
+static struct attribute *shps_power_attrs[] = {
+	&dev_attr_dgpu_power.attr,
+	&dev_attr_dgpu_power_dsm.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(shps_power);
+
+
+static void dbg_dump_power_states(struct platform_device *pdev, const char *prefix)
+{
+	enum shps_dgpu_power power_dsm;
+	enum shps_dgpu_power power_rp;
+	int status;
+
+	status = shps_dgpu_rp_get_power_unlocked(pdev);
+	if (status < 0)
+		dev_err(&pdev->dev, "%s: failed to get root-port power state: %d\n", prefix, status);
+	power_rp = status;
+
+	status = shps_dgpu_rp_get_power_unlocked(pdev);
+	if (status < 0)
+		dev_err(&pdev->dev, "%s: failed to get direct power state: %d\n", prefix, status);
+	power_dsm = status;
+
+	dev_dbg(&pdev->dev, "%s: root-port power state: %d\n", prefix, power_rp);
+	dev_dbg(&pdev->dev, "%s: direct power state:    %d\n", prefix, power_dsm);
+}
+
+static void dbg_dump_pciesta(struct platform_device *pdev, const char *prefix)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	struct pci_dev *rp = drvdata->dgpu_root_port;
+	u16 lnksta, lnksta2, sltsta, sltsta2;
+
+	pcie_capability_read_word(rp, PCI_EXP_LNKSTA, &lnksta);
+	pcie_capability_read_word(rp, PCI_EXP_LNKSTA2, &lnksta2);
+	pcie_capability_read_word(rp, PCI_EXP_SLTSTA, &sltsta);
+	pcie_capability_read_word(rp, PCI_EXP_SLTSTA2, &sltsta2);
+
+	dev_dbg(&pdev->dev, "%s: LNKSTA: 0x%04x\n", prefix, lnksta);
+	dev_dbg(&pdev->dev, "%s: LNKSTA2: 0x%04x\n", prefix, lnksta2);
+	dev_dbg(&pdev->dev, "%s: SLTSTA: 0x%04x\n", prefix, sltsta);
+	dev_dbg(&pdev->dev, "%s: SLTSTA2: 0x%04x\n", prefix, sltsta2);
+}
+
+static void dbg_dump_drvsta(struct platform_device *pdev, const char *prefix)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	struct pci_dev *rp = drvdata->dgpu_root_port;
+
+	dev_dbg(&pdev->dev, "%s: RP power: %d\n", prefix, rp->current_state);
+	dev_dbg(&pdev->dev, "%s: RP state saved: %d\n", prefix, rp->state_saved);
+	dev_dbg(&pdev->dev, "%s: RP state stored: %d\n", prefix, !!drvdata->dgpu_root_port_state);
+	dev_dbg(&pdev->dev, "%s: RP enabled: %d\n", prefix, atomic_read(&rp->enable_cnt));
+	dev_dbg(&pdev->dev, "%s: RP mastered: %d\n", prefix, rp->is_busmaster);
+}
+
+static int shps_pm_prepare(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	bool pwrtgt;
+	int status = 0;
+
+	dbg_dump_power_states(pdev, "shps_pm_prepare");
+
+	if (param_dgpu_power_susp != SHPS_DGPU_MP_POWER_ASIS) {
+		pwrtgt = test_bit(SHPS_STATE_BIT_PWRTGT, &drvdata->state);
+
+		status = shps_dgpu_set_power(pdev, param_dgpu_power_susp);
+		if (status) {
+			dev_err(&pdev->dev, "failed to power %s dGPU: %d\n",
+				param_dgpu_power_susp == SHPS_DGPU_MP_POWER_OFF ? "off" : "on",
+				status);
+			return status;
+		}
+
+		if (pwrtgt)
+			set_bit(SHPS_STATE_BIT_PWRTGT, &drvdata->state);
+		else
+			clear_bit(SHPS_STATE_BIT_PWRTGT, &drvdata->state);
+	}
+
+	return 0;
+}
+
+static void shps_pm_complete(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	int status;
+
+	dbg_dump_power_states(pdev, "shps_pm_complete");
+	dbg_dump_pciesta(pdev, "shps_pm_complete");
+	dbg_dump_drvsta(pdev, "shps_pm_complete.1");
+
+	// update power target, dGPU may have been detached while suspended
+	status = shps_dgpu_is_present(pdev);
+	if (status < 0) {
+		dev_err(&pdev->dev, "failed to get dGPU presence: %d\n", status);
+		return;
+	} else if (status == 0) {
+		clear_bit(SHPS_STATE_BIT_PWRTGT, &drvdata->state);
+	}
+
+	/*
+	 * During resume, the PCIe core will power on the root-port, which in turn
+	 * will power on the dGPU. Most of the state synchronization is already
+	 * handled via the SAN RQSG handler, so it is in a fully consistent
+	 * on-state here. If requested, turn it off here.
+	 *
+	 * As there seem to be some synchronization issues turning off the dGPU
+	 * directly after the power-on SAN RQSG notification during the resume
+	 * process, let's do this here.
+	 *
+	 * TODO/FIXME:
+	 *   This does not combat unhandled power-ons when the device is not fully
+	 *   resumed, i.e. re-suspended before shps_pm_complete is called. Those
+	 *   should normally not be an issue, but the dGPU does get hot even though
+	 *   it is suspended, so ideally we want to keep it off.
+	 */
+	if (!test_bit(SHPS_STATE_BIT_PWRTGT, &drvdata->state)) {
+		status = shps_dgpu_set_power(pdev, SHPS_DGPU_POWER_OFF);
+		if (status)
+			dev_err(&pdev->dev, "failed to power-off dGPU: %d\n", status);
+	}
+
+	dbg_dump_drvsta(pdev, "shps_pm_complete.2");
+}
+
+static int shps_pm_suspend(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	int status;
+
+	if (device_may_wakeup(dev)) {
+		status = enable_irq_wake(drvdata->irq_base_presence);
+		if (status)
+			return status;
+
+		set_bit(SHPS_STATE_BIT_WAKE_ENABLED, &drvdata->state);
+	}
+
+	return 0;
+}
+
+static int shps_pm_resume(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	int status = 0;
+
+	if (test_and_clear_bit(SHPS_STATE_BIT_WAKE_ENABLED, &drvdata->state))
+		status = disable_irq_wake(drvdata->irq_base_presence);
+
+	return status;
+}
+
+static void shps_shutdown(struct platform_device *pdev)
+{
+	int status;
+
+	/*
+	 * Turn on dGPU before shutting down. This allows the core drivers to
+	 * properly shut down the device. If we don't do this, the pcieport driver
+	 * will complain that the device has already been disabled.
+	 */
+	status = shps_dgpu_set_power(pdev, SHPS_DGPU_POWER_ON);
+	if (status)
+		dev_err(&pdev->dev, "failed to turn on dGPU: %d\n", status);
+}
+
+static int shps_dgpu_detached(struct platform_device *pdev)
+{
+	dbg_dump_power_states(pdev, "shps_dgpu_detached");
+	return shps_dgpu_set_power(pdev, SHPS_DGPU_POWER_OFF);
+}
+
+static int shps_dgpu_attached(struct platform_device *pdev)
+{
+	dbg_dump_power_states(pdev, "shps_dgpu_attached");
+	return 0;
+}
+
+static int shps_dgpu_powered_on(struct platform_device *pdev)
+{
+	/*
+	 * This function gets called directly after a power-state transition of
+	 * the dGPU root port out of D3cold state, indicating a power-on of the
+	 * dGPU. Specifically, this function is called from the RQSG handler of
+	 * SAN, invoked by the ACPI _ON method of the dGPU root port. This means
+	 * that this function is run inside `pci_set_power_state(rp, ...)`
+	 * syncrhonously and thus returns before the `pci_set_power_state` call
+	 * does.
+	 *
+	 * `pci_set_power_state` may either be called by us or when the PCI
+	 * subsystem decides to power up the root port (e.g. during resume). Thus
+	 * we should use this function to ensure that the dGPU and root port
+	 * states are consistent when an unexpected power-up is encountered.
+	 */
+
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	struct pci_dev *rp = drvdata->dgpu_root_port;
+	int status;
+
+	dbg_dump_drvsta(pdev, "shps_dgpu_powered_on.1");
+
+	// if we caused the root port to power-on, return
+	if (test_bit(SHPS_STATE_BIT_RPPWRON_SYNC, &drvdata->state))
+		return 0;
+
+	// if dGPU is not present, force power-target to off and return
+	status = shps_dgpu_is_present(pdev);
+	if (status == 0)
+		clear_bit(SHPS_STATE_BIT_PWRTGT, &drvdata->state);
+	if (status <= 0)
+		return status;
+
+	mutex_lock(&drvdata->lock);
+
+	dbg_dump_power_states(pdev, "shps_dgpu_powered_on.1");
+	dbg_dump_pciesta(pdev, "shps_dgpu_powered_on.1");
+	if (drvdata->dgpu_root_port_state)
+		pci_load_and_free_saved_state(rp, &drvdata->dgpu_root_port_state);
+	pci_restore_state(rp);
+	if (!pci_is_enabled(rp))
+		pci_enable_device(rp);
+	pci_set_master(rp);
+	dbg_dump_drvsta(pdev, "shps_dgpu_powered_on.2");
+	dbg_dump_power_states(pdev, "shps_dgpu_powered_on.2");
+	dbg_dump_pciesta(pdev, "shps_dgpu_powered_on.2");
+
+	mutex_unlock(&drvdata->lock);
+
+	if (!test_bit(SHPS_STATE_BIT_PWRTGT, &drvdata->state)) {
+		dev_warn(&pdev->dev, "unexpected dGPU power-on detected\n");
+		// TODO: schedule state re-check and update
+	}
+
+	return 0;
+}
+
+static int shps_dgpu_handle_rqsg(struct surface_sam_san_rqsg *rqsg, void *data)
+{
+	struct platform_device *pdev = data;
+
+	if (rqsg->tc == SAM_DGPU_TC && rqsg->cid == SAM_DGPU_CID_POWERON)
+		return shps_dgpu_powered_on(pdev);
+
+	dev_warn(&pdev->dev, "unimplemented dGPU request: RQSG(0x%02x, 0x%02x, 0x%02x)\n",
+		 rqsg->tc, rqsg->cid, rqsg->iid);
+	return 0;
+}
+
+static irqreturn_t shps_dgpu_presence_irq(int irq, void *data)
+{
+	struct platform_device *pdev = data;
+	bool dgpu_present;
+	int status;
+
+	status = shps_dgpu_is_present(pdev);
+	if (status < 0) {
+		dev_err(&pdev->dev, "failed to check physical dGPU presence: %d\n", status);
+		return IRQ_HANDLED;
+	}
+
+	dgpu_present = status != 0;
+	dev_info(&pdev->dev, "dGPU physically %s\n", dgpu_present ? "attached" : "detached");
+
+	if (dgpu_present)
+		status = shps_dgpu_attached(pdev);
+	else
+		status = shps_dgpu_detached(pdev);
+
+	if (status)
+		dev_err(&pdev->dev, "error handling dGPU interrupt: %d\n", status);
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t shps_base_presence_irq(int irq, void *data)
+{
+	return IRQ_HANDLED;	// nothing to do, just wake
+}
+
+
+static int shps_gpios_setup(struct platform_device *pdev)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	struct gpio_desc *gpio_dgpu_power;
+	struct gpio_desc *gpio_dgpu_presence;
+	struct gpio_desc *gpio_base_presence;
+	int status;
+
+	// get GPIOs
+	gpio_dgpu_power = devm_gpiod_get(&pdev->dev, "dgpu_power", GPIOD_IN);
+	if (IS_ERR(gpio_dgpu_power)) {
+		status = PTR_ERR(gpio_dgpu_power);
+		goto err_out;
+	}
+
+	gpio_dgpu_presence = devm_gpiod_get(&pdev->dev, "dgpu_presence", GPIOD_IN);
+	if (IS_ERR(gpio_dgpu_presence)) {
+		status = PTR_ERR(gpio_dgpu_presence);
+		goto err_out;
+	}
+
+	gpio_base_presence = devm_gpiod_get(&pdev->dev, "base_presence", GPIOD_IN);
+	if (IS_ERR(gpio_base_presence)) {
+		status = PTR_ERR(gpio_base_presence);
+		goto err_out;
+	}
+
+	// export GPIOs
+	status = gpiod_export(gpio_dgpu_power, false);
+	if (status)
+		goto err_out;
+
+	status = gpiod_export(gpio_dgpu_presence, false);
+	if (status)
+		goto err_export_dgpu_presence;
+
+	status = gpiod_export(gpio_base_presence, false);
+	if (status)
+		goto err_export_base_presence;
+
+	// create sysfs links
+	status = gpiod_export_link(&pdev->dev, "gpio-dgpu_power", gpio_dgpu_power);
+	if (status)
+		goto err_link_dgpu_power;
+
+	status = gpiod_export_link(&pdev->dev, "gpio-dgpu_presence", gpio_dgpu_presence);
+	if (status)
+		goto err_link_dgpu_presence;
+
+	status = gpiod_export_link(&pdev->dev, "gpio-base_presence", gpio_base_presence);
+	if (status)
+		goto err_link_base_presence;
+
+	drvdata->gpio_dgpu_power = gpio_dgpu_power;
+	drvdata->gpio_dgpu_presence = gpio_dgpu_presence;
+	drvdata->gpio_base_presence = gpio_base_presence;
+	return 0;
+
+err_link_base_presence:
+	sysfs_remove_link(&pdev->dev.kobj, "gpio-dgpu_presence");
+err_link_dgpu_presence:
+	sysfs_remove_link(&pdev->dev.kobj, "gpio-dgpu_power");
+err_link_dgpu_power:
+	gpiod_unexport(gpio_base_presence);
+err_export_base_presence:
+	gpiod_unexport(gpio_dgpu_presence);
+err_export_dgpu_presence:
+	gpiod_unexport(gpio_dgpu_power);
+err_out:
+	return status;
+}
+
+static void shps_gpios_remove(struct platform_device *pdev)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+
+	sysfs_remove_link(&pdev->dev.kobj, "gpio-base_presence");
+	sysfs_remove_link(&pdev->dev.kobj, "gpio-dgpu_presence");
+	sysfs_remove_link(&pdev->dev.kobj, "gpio-dgpu_power");
+	gpiod_unexport(drvdata->gpio_base_presence);
+	gpiod_unexport(drvdata->gpio_dgpu_presence);
+	gpiod_unexport(drvdata->gpio_dgpu_power);
+}
+
+static int shps_gpios_setup_irq(struct platform_device *pdev)
+{
+	const int irqf_dgpu = IRQF_SHARED | IRQF_ONESHOT | IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING;
+	const int irqf_base = IRQF_SHARED;
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	int status;
+
+	status = gpiod_to_irq(drvdata->gpio_base_presence);
+	if (status < 0)
+		return status;
+	drvdata->irq_base_presence = status;
+
+	status = gpiod_to_irq(drvdata->gpio_dgpu_presence);
+	if (status < 0)
+		return status;
+	drvdata->irq_dgpu_presence = status;
+
+	status = request_irq(drvdata->irq_base_presence,
+			     shps_base_presence_irq, irqf_base,
+			     "shps_base_presence_irq", pdev);
+	if (status) {
+		dev_err(&pdev->dev, "base irq failed: %d\n", status);
+		return status;
+	}
+
+	status = request_threaded_irq(drvdata->irq_dgpu_presence,
+				      NULL, shps_dgpu_presence_irq, irqf_dgpu,
+				      "shps_dgpu_presence_irq", pdev);
+	if (status) {
+		free_irq(drvdata->irq_base_presence, pdev);
+		return status;
+	}
+
+	return 0;
+}
+
+static void shps_gpios_remove_irq(struct platform_device *pdev)
+{
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+
+	free_irq(drvdata->irq_base_presence, pdev);
+	free_irq(drvdata->irq_dgpu_presence, pdev);
+}
+
+static void shps_sgcp_notify(acpi_handle device, u32 value, void *context) {
+	struct platform_device *pdev = context;
+	switch (value) {
+		case ACPI_SGCP_NOTIFY_POWER_ON:
+			shps_dgpu_powered_on(pdev);
+	}
+}
+
+static int shps_start_sgcp_notification(struct platform_device *pdev, acpi_handle *sgpc_handle) {
+	acpi_handle handle;
+	int status;
+
+	status = acpi_get_handle(NULL, "\\_SB.SGPC", &handle);
+	if (status) {
+		dev_err(&pdev->dev, "error in get_handle %d\n", status);
+		return status;
+	}
+
+	status = acpi_install_notify_handler(handle, ACPI_DEVICE_NOTIFY, shps_sgcp_notify, pdev);
+	if (status) {
+		dev_err(&pdev->dev, "error in install notify %d\n", status);
+		*sgpc_handle = NULL;
+		return status;
+	}
+
+	*sgpc_handle = handle;
+	return 0;
+}
+
+static void shps_remove_sgcp_notification(struct platform_device *pdev) {
+	int status;
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+
+	if (drvdata->sgpc_handle) {
+		status = acpi_remove_notify_handler(drvdata->sgpc_handle, ACPI_DEVICE_NOTIFY, shps_sgcp_notify);
+		if (status) {
+			dev_err(&pdev->dev, "failed to remove notify handler: %d\n", status);
+		}
+	}
+}
+
+static struct shps_hardware_traits shps_detect_hardware_traits(struct platform_device *pdev) {
+	const struct shps_hardware_probe *p;
+
+	for (p = shps_hardware_probe_match; p->hardware_id; ++p) {
+		if (acpi_dev_present(p->hardware_id, NULL, -1)) {
+			break;
+		}
+	}
+
+	dev_info(&pdev->dev,
+		"shps_detect_hardware_traits found device %s, generation %d\n",
+		p->hardware_id ? p->hardware_id : "SAN (default)",
+		p->generation);
+
+	return *p->hardware_traits;
+}
+
+static int shps_probe(struct platform_device *pdev)
+{
+	struct acpi_device *shps_dev = ACPI_COMPANION(&pdev->dev);
+	struct shps_driver_data *drvdata;
+	struct ssam_controller *ctrl;
+	struct device_link *link;
+	int power, status;
+	struct shps_hardware_traits detected_traits;
+
+	if (gpiod_count(&pdev->dev, NULL) < 0) {
+		dev_err(&pdev->dev, "gpiod_count returned < 0\n");
+		return -ENODEV;
+	}
+
+	// link to SSH
+	status = ssam_client_bind(&pdev->dev, &ctrl);
+	if (status) {
+		return status == -ENXIO ? -EPROBE_DEFER : status;
+	}
+
+	// detect what kind of hardware we're running
+	detected_traits = shps_detect_hardware_traits(pdev);
+
+	if (detected_traits.notification_method == SHPS_NOTIFICATION_METHOD_SAN) {
+		// link to SAN
+		status = surface_sam_san_consumer_register(&pdev->dev, 0);
+		if (status) {
+			dev_err(&pdev->dev, "failed to register with san consumer: %d\n", status);
+			return status == -ENXIO ? -EPROBE_DEFER : status;
+		}
+	}
+
+	status = acpi_dev_add_driver_gpios(shps_dev, shps_acpi_gpios);
+	if (status) {
+		dev_err(&pdev->dev, "failed to add gpios: %d\n", status);
+		return status;
+	}
+
+	drvdata = kzalloc(sizeof(struct shps_driver_data), GFP_KERNEL);
+	if (!drvdata) {
+		status = -ENOMEM;
+		goto err_drvdata;
+	}
+	mutex_init(&drvdata->lock);
+	platform_set_drvdata(pdev, drvdata);
+
+	drvdata->ctrl = ctrl;
+	drvdata->hardware_traits = detected_traits;
+
+	drvdata->dgpu_root_port = shps_dgpu_dsm_get_pci_dev(pdev);
+	if (IS_ERR(drvdata->dgpu_root_port)) {
+		status = PTR_ERR(drvdata->dgpu_root_port);
+		dev_err(&pdev->dev, "failed to get pci dev: %d\n", status);
+		goto err_rp_lookup;
+	}
+
+	status = shps_gpios_setup(pdev);
+	if (status) {
+		dev_err(&pdev->dev, "unable to set up gpios, %d\n", status);
+		goto err_gpio;
+	}
+
+	status = shps_gpios_setup_irq(pdev);
+	if (status) {
+		dev_err(&pdev->dev, "unable to set up irqs %d\n", status);
+		goto err_gpio_irqs;
+	}
+
+	status = device_add_groups(&pdev->dev, shps_power_groups);
+	if (status)
+		goto err_devattr;
+
+	link = device_link_add(&pdev->dev, &drvdata->dgpu_root_port->dev,
+			       DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER);
+	if (!link)
+		goto err_devlink;
+
+	if (detected_traits.notification_method == SHPS_NOTIFICATION_METHOD_SAN) {
+		status = surface_sam_san_set_rqsg_handler(shps_dgpu_handle_rqsg, pdev);
+		if (status) {
+			dev_err(&pdev->dev, "unable to set SAN notification handler (%d)\n", status);
+			goto err_devlink;
+		}
+	} else if (detected_traits.notification_method == SHPS_NOTIFICATION_METHOD_SGCP) {
+		status = shps_start_sgcp_notification(pdev, &drvdata->sgpc_handle);
+		if (status) {
+			dev_err(&pdev->dev, "unable to install SGCP notification handler (%d)\n", status);
+			goto err_devlink;
+		}
+	}
+
+	// if dGPU is not present turn-off root-port, else obey module param
+	status = shps_dgpu_is_present(pdev);
+	if (status < 0)
+		goto err_post_notification;
+
+	power = status == 0 ? SHPS_DGPU_POWER_OFF : param_dgpu_power_init;
+	if (power != SHPS_DGPU_MP_POWER_ASIS) {
+		status = shps_dgpu_set_power(pdev, power);
+		if (status)
+			goto err_post_notification;
+	}
+
+	// initialize power target
+	status = shps_dgpu_rp_get_power(pdev);
+	if (status < 0)
+		goto err_pwrtgt;
+
+	if (status)
+		set_bit(SHPS_STATE_BIT_PWRTGT, &drvdata->state);
+	else
+		clear_bit(SHPS_STATE_BIT_PWRTGT, &drvdata->state);
+
+	device_init_wakeup(&pdev->dev, true);
+	return 0;
+
+err_pwrtgt:
+	if (param_dgpu_power_exit != SHPS_DGPU_MP_POWER_ASIS) {
+		status = shps_dgpu_set_power(pdev, param_dgpu_power_exit);
+		if (status)
+			dev_err(&pdev->dev, "failed to set dGPU power state: %d\n", status);
+	}
+err_post_notification:
+	if (detected_traits.notification_method == SHPS_NOTIFICATION_METHOD_SGCP) {
+		shps_remove_sgcp_notification(pdev);
+	} else if (detected_traits.notification_method == SHPS_NOTIFICATION_METHOD_SAN) {
+		surface_sam_san_set_rqsg_handler(NULL, NULL);
+	}
+err_devlink:
+	device_remove_groups(&pdev->dev, shps_power_groups);
+err_devattr:
+	shps_gpios_remove_irq(pdev);
+err_gpio_irqs:
+	shps_gpios_remove(pdev);
+err_gpio:
+	pci_dev_put(drvdata->dgpu_root_port);
+err_rp_lookup:
+	platform_set_drvdata(pdev, NULL);
+	kfree(drvdata);
+err_drvdata:
+	acpi_dev_remove_driver_gpios(shps_dev);
+	return status;
+}
+
+static int shps_remove(struct platform_device *pdev)
+{
+	struct acpi_device *shps_dev = ACPI_COMPANION(&pdev->dev);
+	struct shps_driver_data *drvdata = platform_get_drvdata(pdev);
+	int status;
+
+	if (param_dgpu_power_exit != SHPS_DGPU_MP_POWER_ASIS) {
+		status = shps_dgpu_set_power(pdev, param_dgpu_power_exit);
+		if (status)
+			dev_err(&pdev->dev, "failed to set dGPU power state: %d\n", status);
+	}
+
+	device_set_wakeup_capable(&pdev->dev, false);
+
+	if (drvdata->hardware_traits.notification_method == SHPS_NOTIFICATION_METHOD_SGCP) {
+		shps_remove_sgcp_notification(pdev);
+	} else if (drvdata->hardware_traits.notification_method == SHPS_NOTIFICATION_METHOD_SAN) {
+		surface_sam_san_set_rqsg_handler(NULL, NULL);
+	}
+	device_remove_groups(&pdev->dev, shps_power_groups);
+	shps_gpios_remove_irq(pdev);
+	shps_gpios_remove(pdev);
+	pci_dev_put(drvdata->dgpu_root_port);
+	platform_set_drvdata(pdev, NULL);
+	kfree(drvdata);
+
+	acpi_dev_remove_driver_gpios(shps_dev);
+	return 0;
+}
+
+
+static const struct dev_pm_ops shps_pm_ops = {
+	.prepare = shps_pm_prepare,
+	.complete = shps_pm_complete,
+	.suspend = shps_pm_suspend,
+	.resume = shps_pm_resume,
+};
+
+static const struct acpi_device_id shps_acpi_match[] = {
+	{ "MSHW0153", 0 },
+	{ },
+};
+MODULE_DEVICE_TABLE(acpi, shps_acpi_match);
+
+static struct platform_driver surface_sam_hps = {
+	.probe = shps_probe,
+	.remove = shps_remove,
+	.shutdown = shps_shutdown,
+	.driver = {
+		.name = "surface_dgpu_hps",
+		.acpi_match_table = shps_acpi_match,
+		.pm = &shps_pm_ops,
+	},
+};
+
+module_platform_driver(surface_sam_hps);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("Surface Hot-Plug System (HPS) and dGPU power-state Driver for Surface Book 2");
+MODULE_LICENSE("GPL");
diff --git a/drivers/platform/x86/surface_sam/surface_sam_san.c b/drivers/platform/x86/surface_sam/surface_sam_san.c
new file mode 100644
index 000000000000..eab4e178a845
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_san.c
@@ -0,0 +1,930 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Surface ACPI Notify (SAN) and ACPI integration driver for SAM.
+ * Translates communication from ACPI to SSH and back.
+ */
+
+#include <asm/unaligned.h>
+#include <linux/acpi.h>
+#include <linux/delay.h>
+#include <linux/jiffies.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+
+#include "surface_sam_ssh.h"
+#include "surface_sam_san.h"
+
+
+#define SAN_RQST_RETRY				5
+
+#define SAN_DSM_REVISION			0
+#define SAN_DSM_FN_NOTIFY_SENSOR_TRIP_POINT	0x09
+
+static const guid_t SAN_DSM_UUID =
+	GUID_INIT(0x93b666c5, 0x70c6, 0x469f, 0xa2, 0x15, 0x3d,
+		  0x48, 0x7c, 0x91, 0xab, 0x3c);
+
+#define SAM_EVENT_DELAY_PWR_ADAPTER	msecs_to_jiffies(5000)
+#define SAM_EVENT_DELAY_PWR_BST		msecs_to_jiffies(2500)
+
+#define SAM_EVENT_PWR_CID_BIX		0x15
+#define SAM_EVENT_PWR_CID_BST		0x16
+#define SAM_EVENT_PWR_CID_ADAPTER	0x17
+#define SAM_EVENT_PWR_CID_DPTF		0x4f
+
+#define SAM_EVENT_TEMP_CID_NOTIFY_SENSOR_TRIP_POINT	0x0b
+
+
+struct san_acpi_consumer {
+	char *path;
+	bool  required;
+	u32   flags;
+};
+
+struct san_handler_data {
+	struct acpi_connection_info info;		// must be first
+};
+
+struct san_consumer_link {
+	const struct san_acpi_consumer *properties;
+	struct device_link *link;
+};
+
+struct san_consumers {
+	u32 num;
+	struct san_consumer_link *links;
+};
+
+struct san_data {
+	struct device *dev;
+	struct ssam_controller *ctrl;
+
+	struct san_handler_data context;
+	struct san_consumers consumers;
+
+	struct ssam_event_notifier nf_bat;
+	struct ssam_event_notifier nf_tmp;
+};
+
+#define to_san_data(ptr, member) \
+	container_of(ptr, struct san_data, member)
+
+struct san_event_work {
+	struct delayed_work work;
+	struct device *dev;
+	struct ssam_event event;		// must be last
+};
+
+struct gsb_data_in {
+	u8 cv;
+} __packed;
+
+struct gsb_data_rqsx {
+	u8 cv;				// command value (should be 0x01 or 0x03)
+	u8 tc;				// target controller
+	u8 tid;				// transport channnel ID
+	u8 iid;				// target sub-controller (e.g. primary vs. secondary battery)
+	u8 snc;				// expect-response-flag
+	u8 cid;				// command ID
+	u16 cdl;			// payload length
+	u8 pld[0];			// payload
+} __packed;
+
+struct gsb_data_etwl {
+	u8 cv;				// command value (should be 0x02)
+	u8 etw3;			// ?
+	u8 etw4;			// ?
+	u8 msg[0];			// error message (ASCIIZ)
+} __packed;
+
+struct gsb_data_out {
+	u8 status;			// _SSH communication status
+	u8 len;				// _SSH payload length
+	u8 pld[0];			// _SSH payload
+} __packed;
+
+union gsb_buffer_data {
+	struct gsb_data_in   in;	// common input
+	struct gsb_data_rqsx rqsx;	// RQSX input
+	struct gsb_data_etwl etwl;	// ETWL input
+	struct gsb_data_out  out;	// output
+};
+
+struct gsb_buffer {
+	u8 status;			// GSB AttribRawProcess status
+	u8 len;				// GSB AttribRawProcess length
+	union gsb_buffer_data data;
+} __packed;
+
+#define SAN_GSB_MAX_RQSX_PAYLOAD  (U8_MAX - 2 - sizeof(struct gsb_data_rqsx))
+#define SAN_GSB_MAX_RESPONSE	  (U8_MAX - 2 - sizeof(struct gsb_data_out))
+
+#define san_request_sync_onstack(ctrl, rqst, rsp) \
+	ssam_request_sync_onstack(ctrl, rqst, rsp, SAN_GSB_MAX_RQSX_PAYLOAD)
+
+
+enum san_pwr_event {
+	SAN_PWR_EVENT_BAT1_STAT	= 0x03,
+	SAN_PWR_EVENT_BAT1_INFO	= 0x04,
+	SAN_PWR_EVENT_ADP1_STAT	= 0x05,
+	SAN_PWR_EVENT_ADP1_INFO	= 0x06,
+	SAN_PWR_EVENT_BAT2_STAT	= 0x07,
+	SAN_PWR_EVENT_BAT2_INFO	= 0x08,
+	SAN_PWR_EVENT_DPTF      = 0x0A,
+};
+
+
+static int sam_san_default_rqsg_handler(struct surface_sam_san_rqsg *rqsg, void *data);
+
+struct sam_san_rqsg_if {
+	struct mutex lock;
+	struct device *san_dev;
+	surface_sam_san_rqsg_handler_fn handler;
+	void *handler_data;
+};
+
+static struct sam_san_rqsg_if rqsg_if = {
+	.lock = __MUTEX_INITIALIZER(rqsg_if.lock),
+	.san_dev = NULL,
+	.handler = sam_san_default_rqsg_handler,
+	.handler_data = NULL,
+};
+
+int surface_sam_san_consumer_register(struct device *consumer, u32 flags)
+{
+	const u32 valid = DL_FLAG_PM_RUNTIME | DL_FLAG_RPM_ACTIVE;
+	int status;
+
+	if ((flags | valid) != valid)
+		return -EINVAL;
+
+	flags |= DL_FLAG_AUTOREMOVE_CONSUMER;
+
+	mutex_lock(&rqsg_if.lock);
+	if (rqsg_if.san_dev)
+		status = device_link_add(consumer, rqsg_if.san_dev, flags) ? 0 : -EINVAL;
+	else
+		status = -ENXIO;
+	mutex_unlock(&rqsg_if.lock);
+	return status;
+}
+EXPORT_SYMBOL_GPL(surface_sam_san_consumer_register);
+
+int surface_sam_san_set_rqsg_handler(surface_sam_san_rqsg_handler_fn fn, void *data)
+{
+	int status = -EBUSY;
+
+	mutex_lock(&rqsg_if.lock);
+
+	if (rqsg_if.handler == sam_san_default_rqsg_handler || !fn) {
+		rqsg_if.handler = fn ? fn : sam_san_default_rqsg_handler;
+		rqsg_if.handler_data = fn ? data : NULL;
+		status = 0;
+	}
+
+	mutex_unlock(&rqsg_if.lock);
+	return status;
+}
+EXPORT_SYMBOL_GPL(surface_sam_san_set_rqsg_handler);
+
+int san_call_rqsg_handler(struct surface_sam_san_rqsg *rqsg)
+{
+	int status;
+
+	mutex_lock(&rqsg_if.lock);
+	status = rqsg_if.handler(rqsg, rqsg_if.handler_data);
+	mutex_unlock(&rqsg_if.lock);
+
+	return status;
+}
+
+static int sam_san_default_rqsg_handler(struct surface_sam_san_rqsg *rqsg, void *data)
+{
+	struct device *dev = rqsg_if.san_dev;
+
+	dev_warn(dev, "unhandled request: RQSG(0x%02x, 0x%02x, 0x%02x)\n",
+		 rqsg->tc, rqsg->cid, rqsg->iid);
+
+	return 0;
+}
+
+
+static bool san_acpi_can_notify(struct device *dev, u64 func)
+{
+	acpi_handle san = ACPI_HANDLE(dev);
+	return acpi_check_dsm(san, &SAN_DSM_UUID, SAN_DSM_REVISION, 1 << func);
+}
+
+static int san_acpi_notify_power_event(struct device *dev, enum san_pwr_event event)
+{
+	acpi_handle san = ACPI_HANDLE(dev);
+	union acpi_object *obj;
+
+	if (!san_acpi_can_notify(dev, event))
+		return 0;
+
+	dev_dbg(dev, "notify power event 0x%02x\n", event);
+	obj = acpi_evaluate_dsm_typed(san, &SAN_DSM_UUID, SAN_DSM_REVISION,
+				      event, NULL, ACPI_TYPE_BUFFER);
+
+	if (IS_ERR_OR_NULL(obj))
+		return obj ? PTR_ERR(obj) : -ENXIO;
+
+	if (obj->buffer.length != 1 || obj->buffer.pointer[0] != 0) {
+		dev_err(dev, "got unexpected result from _DSM\n");
+		return -EFAULT;
+	}
+
+	ACPI_FREE(obj);
+	return 0;
+}
+
+static int san_acpi_notify_sensor_trip_point(struct device *dev, u8 iid)
+{
+	acpi_handle san = ACPI_HANDLE(dev);
+	union acpi_object *obj;
+	union acpi_object param;
+
+	if (!san_acpi_can_notify(dev, SAN_DSM_FN_NOTIFY_SENSOR_TRIP_POINT))
+		return 0;
+
+	param.type = ACPI_TYPE_INTEGER;
+	param.integer.value = iid;
+
+	obj = acpi_evaluate_dsm_typed(san, &SAN_DSM_UUID, SAN_DSM_REVISION,
+				      SAN_DSM_FN_NOTIFY_SENSOR_TRIP_POINT,
+				      &param, ACPI_TYPE_BUFFER);
+
+	if (IS_ERR_OR_NULL(obj))
+		return obj ? PTR_ERR(obj) : -ENXIO;
+
+	if (obj->buffer.length != 1 || obj->buffer.pointer[0] != 0) {
+		dev_err(dev, "got unexpected result from _DSM\n");
+		return -EFAULT;
+	}
+
+	ACPI_FREE(obj);
+	return 0;
+}
+
+
+static inline int san_evt_power_adapter(struct device *dev, const struct ssam_event *event)
+{
+	int status;
+
+	status = san_acpi_notify_power_event(dev, SAN_PWR_EVENT_ADP1_STAT);
+	if (status)
+		return status;
+
+	/*
+	 * Enusre that the battery states get updated correctly.
+	 * When the battery is fully charged and an adapter is plugged in, it
+	 * sometimes is not updated correctly, instead showing it as charging.
+	 * Explicitly trigger battery updates to fix this.
+	 */
+
+	status = san_acpi_notify_power_event(dev, SAN_PWR_EVENT_BAT1_STAT);
+	if (status)
+		return status;
+
+	return san_acpi_notify_power_event(dev, SAN_PWR_EVENT_BAT2_STAT);
+}
+
+static inline int san_evt_power_bix(struct device *dev, const struct ssam_event *event)
+{
+	enum san_pwr_event evcode;
+
+	if (event->instance_id == 0x02)
+		evcode = SAN_PWR_EVENT_BAT2_INFO;
+	else
+		evcode = SAN_PWR_EVENT_BAT1_INFO;
+
+	return san_acpi_notify_power_event(dev, evcode);
+}
+
+static inline int san_evt_power_bst(struct device *dev, const struct ssam_event *event)
+{
+	enum san_pwr_event evcode;
+
+	if (event->instance_id == 0x02)
+		evcode = SAN_PWR_EVENT_BAT2_STAT;
+	else
+		evcode = SAN_PWR_EVENT_BAT1_STAT;
+
+	return san_acpi_notify_power_event(dev, evcode);
+}
+
+static inline int san_evt_power_dptf(struct device *dev, const struct ssam_event *event)
+{
+	union acpi_object payload;
+	acpi_handle san = ACPI_HANDLE(dev);
+	union acpi_object *obj;
+
+	if (!san_acpi_can_notify(dev, SAN_PWR_EVENT_DPTF))
+		return 0;
+
+	/*
+	 * The Surface ACPI expects a buffer and not a package. It specifically
+	 * checks for ObjectType (Arg3) == 0x03. This will cause a warning in
+	 * acpica/nsarguments.c, but this can safely be ignored.
+	 */
+	payload.type = ACPI_TYPE_BUFFER;
+	payload.buffer.length = event->length;
+	payload.buffer.pointer = (u8 *)&event->data[0];
+
+	dev_dbg(dev, "notify power event 0x%02x\n", event->command_id);
+	obj = acpi_evaluate_dsm_typed(san, &SAN_DSM_UUID, SAN_DSM_REVISION,
+				      SAN_PWR_EVENT_DPTF, &payload,
+				      ACPI_TYPE_BUFFER);
+
+	if (IS_ERR_OR_NULL(obj))
+		return obj ? PTR_ERR(obj) : -ENXIO;
+
+	if (obj->buffer.length != 1 || obj->buffer.pointer[0] != 0) {
+		dev_err(dev, "got unexpected result from _DSM\n");
+		return -EFAULT;
+	}
+
+	ACPI_FREE(obj);
+	return 0;
+}
+
+static unsigned long san_evt_power_delay(u8 cid)
+{
+	switch (cid) {
+	case SAM_EVENT_PWR_CID_ADAPTER:
+		/*
+		 * Wait for battery state to update before signalling adapter change.
+		 */
+		return SAM_EVENT_DELAY_PWR_ADAPTER;
+
+	case SAM_EVENT_PWR_CID_BST:
+		/*
+		 * Ensure we do not miss anything important due to caching.
+		 */
+		return SAM_EVENT_DELAY_PWR_BST;
+
+	case SAM_EVENT_PWR_CID_BIX:
+	case SAM_EVENT_PWR_CID_DPTF:
+	default:
+		return 0;
+	}
+}
+
+static bool san_evt_power(const struct ssam_event *event, struct device *dev)
+{
+	int status;
+
+	switch (event->command_id) {
+	case SAM_EVENT_PWR_CID_BIX:
+		status = san_evt_power_bix(dev, event);
+		break;
+
+	case SAM_EVENT_PWR_CID_BST:
+		status = san_evt_power_bst(dev, event);
+		break;
+
+	case SAM_EVENT_PWR_CID_ADAPTER:
+		status = san_evt_power_adapter(dev, event);
+		break;
+
+	case SAM_EVENT_PWR_CID_DPTF:
+		status = san_evt_power_dptf(dev, event);
+		break;
+
+	default:
+		return false;
+	}
+
+	if (status)
+		dev_err(dev, "error handling power event (cid = %x)\n",
+			event->command_id);
+
+	return true;
+}
+
+static void san_evt_power_workfn(struct work_struct *work)
+{
+	struct san_event_work *ev = container_of(work, struct san_event_work, work.work);
+
+	san_evt_power(&ev->event, ev->dev);
+	kfree(ev);
+}
+
+
+static u32 san_evt_power_nb(struct ssam_notifier_block *nb, const struct ssam_event *event)
+{
+	struct san_data *d = to_san_data(nb, nf_bat.base);
+	struct san_event_work *work;
+	unsigned long delay = san_evt_power_delay(event->command_id);
+
+	if (delay == 0) {
+		if (san_evt_power(event, d->dev))
+			return SSAM_NOTIF_HANDLED;
+		else
+			return 0;
+	}
+
+	work = kzalloc(sizeof(struct san_event_work) + event->length, GFP_KERNEL);
+	if (!work)
+		return ssam_notifier_from_errno(-ENOMEM);
+
+	INIT_DELAYED_WORK(&work->work, san_evt_power_workfn);
+	work->dev = d->dev;
+
+	memcpy(&work->event, event, sizeof(struct ssam_event) + event->length);
+
+	schedule_delayed_work(&work->work, delay);
+	return SSAM_NOTIF_HANDLED;
+}
+
+
+static inline int san_evt_thermal_notify(struct device *dev, const struct ssam_event *event)
+{
+	return san_acpi_notify_sensor_trip_point(dev, event->instance_id);
+}
+
+static bool san_evt_thermal(const struct ssam_event *event, struct device *dev)
+{
+	int status;
+
+	switch (event->command_id) {
+	case SAM_EVENT_TEMP_CID_NOTIFY_SENSOR_TRIP_POINT:
+		status = san_evt_thermal_notify(dev, event);
+		break;
+
+	default:
+		return false;
+	}
+
+	if (status) {
+		dev_err(dev, "error handling thermal event (cid = %x)\n",
+			event->command_id);
+	}
+
+	return true;
+}
+
+static u32 san_evt_thermal_nb(struct ssam_notifier_block *nb, const struct ssam_event *event)
+{
+	if (san_evt_thermal(event, to_san_data(nb, nf_tmp.base)->dev))
+		return SSAM_NOTIF_HANDLED;
+	else
+		return 0;
+}
+
+
+static struct gsb_data_rqsx
+*san_validate_rqsx(struct device *dev, const char *type, struct gsb_buffer *buffer)
+{
+	struct gsb_data_rqsx *rqsx = &buffer->data.rqsx;
+
+	if (buffer->len < 8) {
+		dev_err(dev, "invalid %s package (len = %d)\n",
+			type, buffer->len);
+		return NULL;
+	}
+
+	if (get_unaligned(&rqsx->cdl) != buffer->len - sizeof(struct gsb_data_rqsx)) {
+		dev_err(dev, "bogus %s package (len = %d, cdl = %d)\n",
+			type, buffer->len, get_unaligned(&rqsx->cdl));
+		return NULL;
+	}
+
+	if (get_unaligned(&rqsx->cdl) > SAN_GSB_MAX_RQSX_PAYLOAD) {
+		dev_err(dev, "payload for %s package too large (cdl = %d)\n",
+			type, get_unaligned(&rqsx->cdl));
+		return NULL;
+	}
+
+	if (rqsx->tid != 0x01) {
+		dev_warn(dev, "unsupported %s package (tid = 0x%02x)\n",
+			 type, rqsx->tid);
+		return NULL;
+	}
+
+	return rqsx;
+}
+
+static acpi_status san_etwl(struct san_data *d, struct gsb_buffer *buffer)
+{
+	struct gsb_data_etwl *etwl = &buffer->data.etwl;
+
+	if (buffer->len < 3) {
+		dev_err(d->dev, "invalid ETWL package (len = %d)\n", buffer->len);
+		return AE_OK;
+	}
+
+	dev_err(d->dev, "ETWL(0x%02x, 0x%02x): %.*s\n",
+		etwl->etw3, etwl->etw4,
+		buffer->len - 3, (char *)etwl->msg);
+
+	// indicate success
+	buffer->status = 0x00;
+	buffer->len = 0x00;
+
+	return AE_OK;
+}
+
+static void gsb_response_error(struct gsb_buffer *gsb, int status)
+{
+	gsb->status          = 0x00;
+	gsb->len             = 0x02;
+	gsb->data.out.status = (u8)(-status);
+	gsb->data.out.len    = 0x00;
+}
+
+static void gsb_response_success(struct gsb_buffer *gsb, u8 *ptr, size_t len)
+{
+	gsb->status          = 0x00;
+	gsb->len             = len + 2;
+	gsb->data.out.status = 0x00;
+	gsb->data.out.len    = len;
+
+	if (len)
+		memcpy(&gsb->data.out.pld[0], ptr, len);
+}
+
+static acpi_status san_rqst_fixup_suspended(struct ssam_request *rqst,
+					    struct gsb_buffer *gsb)
+{
+	if (rqst->target_category == 0x11 && rqst->command_id == 0x0D) {
+		/* Base state quirk:
+		 * The base state may be queried from ACPI when the EC is still
+		 * suspended. In this case it will return '-EPERM'. This query
+		 * will only be triggered from the ACPI lid GPE interrupt, thus
+		 * we are either in laptop or studio mode (base status 0x01 or
+		 * 0x02). Furthermore, we will only get here if the device (and
+		 * EC) have been suspended.
+		 *
+		 * We now assume that the device is in laptop mode (0x01). This
+		 * has the drawback that it will wake the device when unfolding
+		 * it in studio mode, but it also allows us to avoid actively
+		 * waiting for the EC to wake up, which may incur a notable
+		 * delay.
+		 */
+
+		u8 base_state = 1;
+		gsb_response_success(gsb, &base_state, 1);
+		return AE_OK;
+	}
+
+	gsb_response_error(gsb, -ENXIO);
+	return AE_OK;
+}
+
+static acpi_status san_rqst(struct san_data *d, struct gsb_buffer *buffer)
+{
+	u8 rspbuf[SAN_GSB_MAX_RESPONSE];
+	struct gsb_data_rqsx *gsb_rqst;
+	struct ssam_request rqst;
+	struct ssam_response rsp;
+	int status = 0;
+	int try;
+
+ 	gsb_rqst = san_validate_rqsx(d->dev, "RQST", buffer);
+	if (!gsb_rqst)
+		return AE_OK;
+
+	rqst.target_category  = gsb_rqst->tc;
+	rqst.command_id = gsb_rqst->cid;
+	rqst.instance_id = gsb_rqst->iid;
+	rqst.channel = gsb_rqst->tid;
+	rqst.flags = gsb_rqst->snc ? SSAM_REQUEST_HAS_RESPONSE : 0;
+	rqst.length = get_unaligned(&gsb_rqst->cdl);
+	rqst.payload = &gsb_rqst->pld[0];
+
+	rsp.capacity = ARRAY_SIZE(rspbuf);
+	rsp.length  = 0;
+	rsp.pointer = &rspbuf[0];
+
+	// handle suspended device
+	if (d->dev->power.is_suspended) {
+		dev_warn(d->dev, "rqst: device is suspended, not executing\n");
+		return san_rqst_fixup_suspended(&rqst, buffer);
+	}
+
+	for (try = 0; try < SAN_RQST_RETRY; try++) {
+		if (try)
+			dev_warn(d->dev, "rqst: IO error, trying again\n");
+
+		status = san_request_sync_onstack(d->ctrl, &rqst, &rsp);
+		if (status != -ETIMEDOUT && status != -EREMOTEIO)
+			break;
+	}
+
+	if (!status) {
+		gsb_response_success(buffer, rsp.pointer, rsp.length);
+	} else {
+		dev_err(d->dev, "rqst: failed with error %d\n", status);
+		gsb_response_error(buffer, status);
+	}
+
+	return AE_OK;
+}
+
+static acpi_status san_rqsg(struct san_data *d, struct gsb_buffer *buffer)
+{
+	struct gsb_data_rqsx *gsb_rqsg;
+	struct surface_sam_san_rqsg rqsg;
+	int status;
+
+	gsb_rqsg = san_validate_rqsx(d->dev, "RQSG", buffer);
+	if (!gsb_rqsg)
+		return AE_OK;
+
+	rqsg.tc  = gsb_rqsg->tc;
+	rqsg.cid = gsb_rqsg->cid;
+	rqsg.iid = gsb_rqsg->iid;
+	rqsg.cdl = get_unaligned(&gsb_rqsg->cdl);
+	rqsg.pld = &gsb_rqsg->pld[0];
+
+	status = san_call_rqsg_handler(&rqsg);
+	if (!status) {
+		gsb_response_success(buffer, NULL, 0);
+	} else {
+		dev_err(d->dev, "rqsg: failed with error %d\n", status);
+		gsb_response_error(buffer, status);
+	}
+
+	return AE_OK;
+}
+
+
+static acpi_status
+san_opreg_handler(u32 function, acpi_physical_address command,
+		  u32 bits, u64 *value64,
+		  void *opreg_context, void *region_context)
+{
+	struct san_data *d = to_san_data(opreg_context, context);
+	struct gsb_buffer *buffer = (struct gsb_buffer *)value64;
+	int accessor_type = (0xFFFF0000 & function) >> 16;
+
+	if (command != 0) {
+		dev_warn(d->dev, "unsupported command: 0x%02llx\n", command);
+		return AE_OK;
+	}
+
+	if (accessor_type != ACPI_GSB_ACCESS_ATTRIB_RAW_PROCESS) {
+		dev_err(d->dev, "invalid access type: 0x%02x\n", accessor_type);
+		return AE_OK;
+	}
+
+	// buffer must have at least contain the command-value
+	if (buffer->len == 0) {
+		dev_err(d->dev, "request-package too small\n");
+		return AE_OK;
+	}
+
+	switch (buffer->data.in.cv) {
+	case 0x01:  return san_rqst(d, buffer);
+	case 0x02:  return san_etwl(d, buffer);
+	case 0x03:  return san_rqsg(d, buffer);
+	}
+
+	dev_warn(d->dev, "unsupported SAN0 request (cv: 0x%02x)\n", buffer->data.in.cv);
+	return AE_OK;
+}
+
+static int san_events_register(struct platform_device *pdev)
+{
+	struct san_data *d = platform_get_drvdata(pdev);
+	int status;
+
+	d->nf_bat.base.priority = 1;
+	d->nf_bat.base.fn = san_evt_power_nb;
+	d->nf_bat.event.reg = SSAM_EVENT_REGISTRY_SAM;
+	d->nf_bat.event.id.target_category = SSAM_SSH_TC_BAT;
+	d->nf_bat.event.id.instance = 0;
+	d->nf_bat.event.flags = SSAM_EVENT_SEQUENCED;
+
+	d->nf_tmp.base.priority = 1;
+	d->nf_tmp.base.fn = san_evt_thermal_nb;
+	d->nf_tmp.event.reg = SSAM_EVENT_REGISTRY_SAM;
+	d->nf_tmp.event.id.target_category = SSAM_SSH_TC_TMP;
+	d->nf_tmp.event.id.instance = 0;
+	d->nf_tmp.event.flags = SSAM_EVENT_SEQUENCED;
+
+	status = ssam_notifier_register(d->ctrl, &d->nf_bat);
+	if (status)
+		return status;
+
+	status = ssam_notifier_register(d->ctrl, &d->nf_tmp);
+	if (status)
+		ssam_notifier_unregister(d->ctrl, &d->nf_bat);
+
+	return status;
+}
+
+static void san_events_unregister(struct platform_device *pdev)
+{
+	struct san_data *d = platform_get_drvdata(pdev);
+
+	ssam_notifier_unregister(d->ctrl, &d->nf_bat);
+	ssam_notifier_unregister(d->ctrl, &d->nf_tmp);
+}
+
+
+static int san_consumers_link(struct platform_device *pdev,
+			      const struct san_acpi_consumer *cons,
+			      struct san_consumers *out)
+{
+	const struct san_acpi_consumer *con;
+	struct san_consumer_link *links, *link;
+	struct acpi_device *adev;
+	acpi_handle handle;
+	u32 max_links = 0;
+	int status;
+
+	if (!cons)
+		return 0;
+
+	// count links
+	for (con = cons; con->path; ++con)
+		max_links += 1;
+
+	// allocate
+	links = kcalloc(max_links, sizeof(struct san_consumer_link), GFP_KERNEL);
+	link = &links[0];
+
+	if (!links)
+		return -ENOMEM;
+
+	// create links
+	for (con = cons; con->path; ++con) {
+		status = acpi_get_handle(NULL, con->path, &handle);
+		if (status) {
+			if (con->required || status != AE_NOT_FOUND) {
+				status = -ENXIO;
+				goto cleanup;
+			} else {
+				continue;
+			}
+		}
+
+		status = acpi_bus_get_device(handle, &adev);
+		if (status)
+			goto cleanup;
+
+		link->link = device_link_add(&adev->dev, &pdev->dev, con->flags);
+		if (!(link->link)) {
+			status = -EFAULT;
+			goto cleanup;
+		}
+		link->properties = con;
+
+		link += 1;
+	}
+
+	out->num = link - links;
+	out->links = links;
+
+	return 0;
+
+cleanup:
+	for (link = link - 1; link >= links; --link) {
+		if (link->properties->flags & DL_FLAG_STATELESS)
+			device_link_del(link->link);
+	}
+
+	return status;
+}
+
+static void san_consumers_unlink(struct san_consumers *consumers)
+{
+	u32 i;
+
+	if (!consumers)
+		return;
+
+	for (i = 0; i < consumers->num; ++i) {
+		if (consumers->links[i].properties->flags & DL_FLAG_STATELESS)
+			device_link_del(consumers->links[i].link);
+	}
+
+	kfree(consumers->links);
+
+	consumers->num = 0;
+	consumers->links = NULL;
+}
+
+static int surface_sam_san_probe(struct platform_device *pdev)
+{
+	const struct san_acpi_consumer *cons;
+	acpi_handle san = ACPI_HANDLE(&pdev->dev);	// _SAN device node
+	struct ssam_controller *ctrl;
+	struct san_data *data;
+	int status;
+
+	status = ssam_client_bind(&pdev->dev, &ctrl);
+	if (status)
+		return status == -ENXIO ? -EPROBE_DEFER : status;
+
+	data = kzalloc(sizeof(struct san_data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->dev = &pdev->dev;
+	data->ctrl = ctrl;
+
+	cons = acpi_device_get_match_data(&pdev->dev);
+	status = san_consumers_link(pdev, cons, &data->consumers);
+	if (status)
+		goto err_consumers;
+
+	platform_set_drvdata(pdev, data);
+
+	status = acpi_install_address_space_handler(san,
+			ACPI_ADR_SPACE_GSBUS,
+			&san_opreg_handler,
+			NULL, &data->context);
+
+	if (ACPI_FAILURE(status)) {
+		status = -ENODEV;
+		goto err_install_handler;
+	}
+
+	status = san_events_register(pdev);
+	if (status)
+		goto err_enable_events;
+
+	mutex_lock(&rqsg_if.lock);
+	if (!rqsg_if.san_dev)
+		rqsg_if.san_dev = &pdev->dev;
+	else
+		status = -EBUSY;
+	mutex_unlock(&rqsg_if.lock);
+
+	if (status)
+		goto err_install_dev;
+
+	acpi_walk_dep_device_list(san);
+	return 0;
+
+err_install_dev:
+	san_events_unregister(pdev);
+err_enable_events:
+	acpi_remove_address_space_handler(san, ACPI_ADR_SPACE_GSBUS, &san_opreg_handler);
+err_install_handler:
+	platform_set_drvdata(san, NULL);
+	san_consumers_unlink(&data->consumers);
+err_consumers:
+	kfree(data);
+	return status;
+}
+
+static int surface_sam_san_remove(struct platform_device *pdev)
+{
+	struct san_data *data = platform_get_drvdata(pdev);
+	acpi_handle san = ACPI_HANDLE(&pdev->dev);	// _SAN device node
+	acpi_status status = AE_OK;
+
+	mutex_lock(&rqsg_if.lock);
+	rqsg_if.san_dev = NULL;
+	mutex_unlock(&rqsg_if.lock);
+
+	acpi_remove_address_space_handler(san, ACPI_ADR_SPACE_GSBUS, &san_opreg_handler);
+	san_events_unregister(pdev);
+
+	/*
+	 * We have unregistered our event sources. Now we need to ensure that
+	 * all delayed works they may have spawned are run to completion.
+	 */
+	flush_scheduled_work();
+
+	san_consumers_unlink(&data->consumers);
+	kfree(data);
+
+	platform_set_drvdata(pdev, NULL);
+	return status;
+}
+
+
+static const struct san_acpi_consumer san_mshw0091_consumers[] = {
+	{ "\\_SB.SRTC", true,  DL_FLAG_PM_RUNTIME | DL_FLAG_STATELESS },
+	{ "\\ADP1",     true,  DL_FLAG_PM_RUNTIME | DL_FLAG_STATELESS },
+	{ "\\_SB.BAT1", true,  DL_FLAG_PM_RUNTIME | DL_FLAG_STATELESS },
+	{ "\\_SB.BAT2", false, DL_FLAG_PM_RUNTIME | DL_FLAG_STATELESS },
+	{ },
+};
+
+static const struct acpi_device_id surface_sam_san_match[] = {
+	{ "MSHW0091", (unsigned long) san_mshw0091_consumers },
+	{ },
+};
+MODULE_DEVICE_TABLE(acpi, surface_sam_san_match);
+
+static struct platform_driver surface_sam_san = {
+	.probe = surface_sam_san_probe,
+	.remove = surface_sam_san_remove,
+	.driver = {
+		.name = "surface_sam_san",
+		.acpi_match_table = surface_sam_san_match,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+module_platform_driver(surface_sam_san);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("Surface ACPI Notify Driver for 5th Generation Surface Devices");
+MODULE_LICENSE("GPL");
diff --git a/drivers/platform/x86/surface_sam/surface_sam_san.h b/drivers/platform/x86/surface_sam/surface_sam_san.h
new file mode 100644
index 000000000000..3408dde964b3
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_san.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Interface for Surface ACPI/Notify (SAN).
+ *
+ * The SAN is the main interface between the Surface Serial Hub (SSH) and the
+ * Surface/System Aggregator Module (SAM). It allows requests to be translated
+ * from ACPI to SSH/SAM. It also interfaces with the discrete GPU hot-plug
+ * driver.
+ */
+
+#ifndef _SURFACE_SAM_SAN_H
+#define _SURFACE_SAM_SAN_H
+
+#include <linux/types.h>
+
+
+struct surface_sam_san_rqsg {
+	u8 tc;				// target category
+	u8 cid;				// command ID
+	u8 iid;				// instance ID
+	u16 cdl;			// command data length (length of payload)
+	u8 *pld;			// pointer to payload of length cdl
+};
+
+typedef int (*surface_sam_san_rqsg_handler_fn)(struct surface_sam_san_rqsg *rqsg, void *data);
+
+int surface_sam_san_consumer_register(struct device *consumer, u32 flags);
+int surface_sam_san_set_rqsg_handler(surface_sam_san_rqsg_handler_fn fn, void *data);
+
+#endif /* _SURFACE_SAM_SAN_H */
diff --git a/drivers/platform/x86/surface_sam/surface_sam_sid.c b/drivers/platform/x86/surface_sam/surface_sam_sid.c
new file mode 100644
index 000000000000..bcf9a569ee71
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_sid.c
@@ -0,0 +1,283 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Surface Integration Driver.
+ * MFD driver to provide device/model dependent functionality.
+ */
+
+#include <linux/acpi.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/mfd/core.h>
+
+#include "surface_sam_sid_power.h"
+#include "surface_sam_sid_vhf.h"
+
+
+static const struct ssam_battery_properties ssam_battery_props_bat1 = {
+	.registry = SSAM_EVENT_REGISTRY_SAM,
+	.num      = 0,
+	.channel  = 1,
+	.instance = 1,
+};
+
+static const struct ssam_battery_properties ssam_battery_props_bat2_sb3 = {
+	.registry = SSAM_EVENT_REGISTRY_KIP,
+	.num      = 1,
+	.channel  = 2,
+	.instance = 1,
+};
+
+
+static const struct ssam_hid_properties ssam_hid_props_keyboard = {
+	.registry = SSAM_EVENT_REGISTRY_REG,
+	.instance = 1,
+};
+
+static const struct ssam_hid_properties ssam_hid_props_touchpad = {
+	.registry = SSAM_EVENT_REGISTRY_REG,
+	.instance = 3,
+};
+
+static const struct ssam_hid_properties ssam_hid_props_iid5 = {
+	.registry = SSAM_EVENT_REGISTRY_REG,
+	.instance = 5,
+};
+
+static const struct ssam_hid_properties ssam_hid_props_iid6 = {
+	.registry = SSAM_EVENT_REGISTRY_REG,
+	.instance = 6,
+};
+
+
+static const struct mfd_cell sid_devs_sp4[] = {
+	{ .name = "surface_sam_sid_gpelid",   .id = -1 },
+	{ .name = "surface_sam_sid_perfmode", .id = -1 },
+	{ },
+};
+
+static const struct mfd_cell sid_devs_sp6[] = {
+	{ .name = "surface_sam_sid_gpelid",   .id = -1 },
+	{ .name = "surface_sam_sid_perfmode", .id = -1 },
+	{ },
+};
+
+static const struct mfd_cell sid_devs_sp7[] = {
+	{ .name = "surface_sam_sid_gpelid",   .id = -1 },
+	{ .name = "surface_sam_sid_perfmode", .id = -1 },
+	{ .name = "surface_sam_sid_ac",       .id = -1 },
+	{
+		.name = "surface_sam_sid_battery",
+		.id = -1,
+		.platform_data = (void *)&ssam_battery_props_bat1,
+		.pdata_size = sizeof(struct ssam_battery_properties),
+	},
+	{ },
+};
+
+static const struct mfd_cell sid_devs_sb1[] = {
+	{ .name = "surface_sam_sid_gpelid", .id = -1 },
+	{ },
+};
+
+static const struct mfd_cell sid_devs_sb2[] = {
+	{ .name = "surface_sam_sid_gpelid",   .id = -1 },
+	{ .name = "surface_sam_sid_perfmode", .id = -1 },
+	{ },
+};
+
+static const struct mfd_cell sid_devs_sb3[] = {
+	{ .name = "surface_sam_sid_gpelid",   .id = -1 },
+	{ .name = "surface_sam_sid_perfmode", .id = -1 },
+	{ .name = "surface_sam_sid_ac",       .id = -1 },
+	{
+		.name = "surface_sam_sid_battery",
+		.id = 1,
+		.platform_data = (void *)&ssam_battery_props_bat1,
+		.pdata_size = sizeof(struct ssam_battery_properties),
+	},
+	{
+		.name = "surface_sam_sid_battery",
+		.id = 2,
+		.platform_data = (void *)&ssam_battery_props_bat2_sb3,
+		.pdata_size = sizeof(struct ssam_battery_properties),
+	},
+	{
+		.name = "surface_sam_sid_vhf",
+		.id = 1,
+		.platform_data = (void *)&ssam_hid_props_keyboard,
+		.pdata_size = sizeof(struct ssam_hid_properties),
+	},
+	{
+		.name = "surface_sam_sid_vhf",
+		.id = 3,
+		.platform_data = (void *)&ssam_hid_props_touchpad,
+		.pdata_size = sizeof(struct ssam_hid_properties),
+	},
+	{
+		.name = "surface_sam_sid_vhf",
+		.id = 5,
+		.platform_data = (void *)&ssam_hid_props_iid5,
+		.pdata_size = sizeof(struct ssam_hid_properties),
+	},
+	{
+		.name = "surface_sam_sid_vhf",
+		.id = 6,
+		.platform_data = (void *)&ssam_hid_props_iid6,
+		.pdata_size = sizeof(struct ssam_hid_properties),
+	},
+	{ },
+};
+
+static const struct mfd_cell sid_devs_sl1[] = {
+	{ .name = "surface_sam_sid_gpelid",   .id = -1 },
+	{ .name = "surface_sam_sid_perfmode", .id = -1 },
+	{ },
+};
+
+static const struct mfd_cell sid_devs_sl2[] = {
+	{ .name = "surface_sam_sid_gpelid",   .id = -1 },
+	{ .name = "surface_sam_sid_perfmode", .id = -1 },
+	{ },
+};
+
+static const struct mfd_cell sid_devs_sl3_13[] = {
+	{ .name = "surface_sam_sid_gpelid",   .id = -1 },
+	{ .name = "surface_sam_sid_perfmode", .id = -1 },
+	{ .name = "surface_sam_sid_ac",       .id = -1 },
+	{
+		.name = "surface_sam_sid_battery",
+		.id = -1,
+		.platform_data = (void *)&ssam_battery_props_bat1,
+		.pdata_size = sizeof(struct ssam_battery_properties),
+	},
+	{
+		.name = "surface_sam_sid_vhf",
+		.id = 1,
+		.platform_data = (void *)&ssam_hid_props_keyboard,
+		.pdata_size = sizeof(struct ssam_hid_properties),
+	},
+	{
+		.name = "surface_sam_sid_vhf",
+		.id = 3,
+		.platform_data = (void *)&ssam_hid_props_touchpad,
+		.pdata_size = sizeof(struct ssam_hid_properties),
+	},
+	{
+		.name = "surface_sam_sid_vhf",
+		.id = 5,
+		.platform_data = (void *)&ssam_hid_props_iid5,
+		.pdata_size = sizeof(struct ssam_hid_properties),
+	},
+	{ },
+};
+
+static const struct mfd_cell sid_devs_sl3_15[] = {
+	{ .name = "surface_sam_sid_perfmode", .id = -1 },
+	{ .name = "surface_sam_sid_ac",       .id = -1 },
+	{
+		.name = "surface_sam_sid_battery",
+		.id = -1,
+		.platform_data = (void *)&ssam_battery_props_bat1,
+		.pdata_size = sizeof(struct ssam_battery_properties),
+	},
+	{
+		.name = "surface_sam_sid_vhf",
+		.id = 1,
+		.platform_data = (void *)&ssam_hid_props_keyboard,
+		.pdata_size = sizeof(struct ssam_hid_properties),
+	},
+	{
+		.name = "surface_sam_sid_vhf",
+		.id = 3,
+		.platform_data = (void *)&ssam_hid_props_touchpad,
+		.pdata_size = sizeof(struct ssam_hid_properties),
+	},
+	{
+		.name = "surface_sam_sid_vhf",
+		.id = 5,
+		.platform_data = (void *)&ssam_hid_props_iid5,
+		.pdata_size = sizeof(struct ssam_hid_properties),
+	},
+	{ },
+};
+
+static const struct acpi_device_id surface_sam_sid_match[] = {
+	/* Surface Pro 4, 5, and 6 */
+	{ "MSHW0081", (unsigned long)sid_devs_sp4 },
+
+	/* Surface Pro 6 (OMBR >= 0x10) */
+	{ "MSHW0111", (unsigned long)sid_devs_sp6 },
+
+	/* Surface Pro 7 */
+	{ "MSHW0116", (unsigned long)sid_devs_sp7 },
+
+	/* Surface Book 1 */
+	{ "MSHW0080", (unsigned long)sid_devs_sb1 },
+
+	/* Surface Book 2 */
+	{ "MSHW0107", (unsigned long)sid_devs_sb2 },
+
+	/* Surface Book 3 */
+	{ "MSHW0117", (unsigned long)sid_devs_sb3 },
+
+	/* Surface Laptop 1 */
+	{ "MSHW0086", (unsigned long)sid_devs_sl1 },
+
+	/* Surface Laptop 2 */
+	{ "MSHW0112", (unsigned long)sid_devs_sl2 },
+
+	/* Surface Laptop 3 (13") */
+	{ "MSHW0114", (unsigned long)sid_devs_sl3_13 },
+
+	/* Surface Laptop 3 (15") */
+	{ "MSHW0110", (unsigned long)sid_devs_sl3_15 },
+
+	{ },
+};
+MODULE_DEVICE_TABLE(acpi, surface_sam_sid_match);
+
+
+static int surface_sam_sid_probe(struct platform_device *pdev)
+{
+	const struct acpi_device_id *match;
+	const struct mfd_cell *cells, *p;
+
+	match = acpi_match_device(surface_sam_sid_match, &pdev->dev);
+	if (!match)
+		return -ENODEV;
+
+	cells = (struct mfd_cell *)match->driver_data;
+	if (!cells)
+		return -ENODEV;
+
+	for (p = cells; p->name; ++p) {
+		/* just count */
+	}
+
+	if (p == cells)
+		return -ENODEV;
+
+	return mfd_add_devices(&pdev->dev, 0, cells, p - cells, NULL, 0, NULL);
+}
+
+static int surface_sam_sid_remove(struct platform_device *pdev)
+{
+	mfd_remove_devices(&pdev->dev);
+	return 0;
+}
+
+static struct platform_driver surface_sam_sid = {
+	.probe = surface_sam_sid_probe,
+	.remove = surface_sam_sid_remove,
+	.driver = {
+		.name = "surface_sam_sid",
+		.acpi_match_table = surface_sam_sid_match,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+module_platform_driver(surface_sam_sid);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("Surface Integration Driver for 5th Generation Surface Devices");
+MODULE_LICENSE("GPL");
diff --git a/drivers/platform/x86/surface_sam/surface_sam_sid_gpelid.c b/drivers/platform/x86/surface_sam/surface_sam_sid_gpelid.c
new file mode 100644
index 000000000000..f0cee43c859b
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_sid_gpelid.c
@@ -0,0 +1,232 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Surface Lid driver to enable wakeup from suspend via the lid.
+ */
+
+#include <linux/acpi.h>
+#include <linux/dmi.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+
+struct sid_lid_device {
+	const char *acpi_path;
+	const u32 gpe_number;
+};
+
+
+static const struct sid_lid_device lid_device_l17 = {
+	.acpi_path = "\\_SB.LID0",
+	.gpe_number = 0x17,
+};
+
+static const struct sid_lid_device lid_device_l4D = {
+	.acpi_path = "\\_SB.LID0",
+	.gpe_number = 0x4D,
+};
+
+static const struct sid_lid_device lid_device_l4F = {
+	.acpi_path = "\\_SB.LID0",
+	.gpe_number = 0x4F,
+};
+
+static const struct sid_lid_device lid_device_l57 = {
+	.acpi_path = "\\_SB.LID0",
+	.gpe_number = 0x57,
+};
+
+
+static const struct dmi_system_id dmi_lid_device_table[] = {
+	{
+		.ident = "Surface Pro 4",
+		.matches = {
+			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
+			DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "Surface Pro 4"),
+		},
+		.driver_data = (void *)&lid_device_l17,
+	},
+	{
+		.ident = "Surface Pro 5",
+		.matches = {
+			/* match for SKU here due to generic product name "Surface Pro" */
+			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
+			DMI_EXACT_MATCH(DMI_PRODUCT_SKU, "Surface_Pro_1796"),
+		},
+		.driver_data = (void *)&lid_device_l4F,
+	},
+	{
+		.ident = "Surface Pro 5 (LTE)",
+		.matches = {
+			/* match for SKU here due to generic product name "Surface Pro" */
+			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
+			DMI_EXACT_MATCH(DMI_PRODUCT_SKU, "Surface_Pro_1807"),
+		},
+		.driver_data = (void *)&lid_device_l4F,
+	},
+	{
+		.ident = "Surface Pro 6",
+		.matches = {
+			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
+			DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "Surface Pro 6"),
+		},
+		.driver_data = (void *)&lid_device_l4F,
+	},
+	{
+		.ident = "Surface Pro 7",
+		.matches = {
+			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
+			DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "Surface Pro 7"),
+		},
+		.driver_data = (void *)&lid_device_l4D,
+	},
+	{
+		.ident = "Surface Book 1",
+		.matches = {
+			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
+			DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "Surface Book"),
+		},
+		.driver_data = (void *)&lid_device_l17,
+	},
+	{
+		.ident = "Surface Book 2",
+		.matches = {
+			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
+			DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "Surface Book 2"),
+		},
+		.driver_data = (void *)&lid_device_l17,
+	},
+	{
+		.ident = "Surface Book 3",
+		.matches = {
+			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
+			DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "Surface Book 3"),
+		},
+		.driver_data = (void *)&lid_device_l4D,
+	},
+	{
+		.ident = "Surface Laptop 1",
+		.matches = {
+			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
+			DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "Surface Laptop"),
+		},
+		.driver_data = (void *)&lid_device_l57,
+	},
+	{
+		.ident = "Surface Laptop 2",
+		.matches = {
+			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
+			DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "Surface Laptop 2"),
+		},
+		.driver_data = (void *)&lid_device_l57,
+	},
+	{
+		.ident = "Surface Laptop 3 (13\")",
+		.matches = {
+			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
+			DMI_EXACT_MATCH(DMI_PRODUCT_SKU, "Surface_Laptop_3_1867:1868"),
+		},
+		.driver_data = (void *)&lid_device_l4D,
+	},
+	{ }
+};
+
+
+static int sid_lid_enable_wakeup(const struct sid_lid_device *dev, bool enable)
+{
+	int action = enable ? ACPI_GPE_ENABLE : ACPI_GPE_DISABLE;
+	int status;
+
+	status = acpi_set_gpe_wake_mask(NULL, dev->gpe_number, action);
+	if (status)
+		return -EFAULT;
+
+	return 0;
+}
+
+
+static int surface_sam_sid_gpelid_suspend(struct device *dev)
+{
+	const struct sid_lid_device *ldev;
+
+	ldev = dev_get_drvdata(dev);
+	return sid_lid_enable_wakeup(ldev, true);
+}
+
+static int surface_sam_sid_gpelid_resume(struct device *dev)
+{
+	const struct sid_lid_device *ldev;
+
+	ldev = dev_get_drvdata(dev);
+	return sid_lid_enable_wakeup(ldev, false);
+}
+
+static SIMPLE_DEV_PM_OPS(surface_sam_sid_gpelid_pm,
+			 surface_sam_sid_gpelid_suspend,
+			 surface_sam_sid_gpelid_resume);
+
+
+static int surface_sam_sid_gpelid_probe(struct platform_device *pdev)
+{
+	const struct dmi_system_id *match;
+	struct sid_lid_device *dev;
+	acpi_handle lid_handle;
+	int status;
+
+	match = dmi_first_match(dmi_lid_device_table);
+	if (!match)
+		return -ENODEV;
+
+	dev = match->driver_data;
+	if (!dev)
+		return -ENODEV;
+
+	status = acpi_get_handle(NULL, (acpi_string)dev->acpi_path, &lid_handle);
+	if (status)
+		return -EFAULT;
+
+	status = acpi_setup_gpe_for_wake(lid_handle, NULL, dev->gpe_number);
+	if (status)
+		return -EFAULT;
+
+	status = acpi_enable_gpe(NULL, dev->gpe_number);
+	if (status)
+		return -EFAULT;
+
+	status = sid_lid_enable_wakeup(dev, false);
+	if (status) {
+		acpi_disable_gpe(NULL, dev->gpe_number);
+		return status;
+	}
+
+	platform_set_drvdata(pdev, dev);
+	return 0;
+}
+
+static int surface_sam_sid_gpelid_remove(struct platform_device *pdev)
+{
+	struct sid_lid_device *dev = platform_get_drvdata(pdev);
+
+	/* restore default behavior without this module */
+	sid_lid_enable_wakeup(dev, false);
+	acpi_disable_gpe(NULL, dev->gpe_number);
+
+	platform_set_drvdata(pdev, NULL);
+	return 0;
+}
+
+static struct platform_driver surface_sam_sid_gpelid = {
+	.probe = surface_sam_sid_gpelid_probe,
+	.remove = surface_sam_sid_gpelid_remove,
+	.driver = {
+		.name = "surface_sam_sid_gpelid",
+		.pm = &surface_sam_sid_gpelid_pm,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+module_platform_driver(surface_sam_sid_gpelid);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("Surface Lid Driver for 5th Generation Surface Devices");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:surface_sam_sid_gpelid");
diff --git a/drivers/platform/x86/surface_sam/surface_sam_sid_perfmode.c b/drivers/platform/x86/surface_sam/surface_sam_sid_perfmode.c
new file mode 100644
index 000000000000..e0b1e42c2087
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_sid_perfmode.c
@@ -0,0 +1,214 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Surface Performance Mode Driver.
+ * Allows to change cooling capabilities based on user preference.
+ */
+
+#include <asm/unaligned.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#include "surface_sam_ssh.h"
+
+
+#define SID_PARAM_PERM		0644
+
+enum sam_perf_mode {
+	SAM_PERF_MODE_NORMAL   = 1,
+	SAM_PERF_MODE_BATTERY  = 2,
+	SAM_PERF_MODE_PERF1    = 3,
+	SAM_PERF_MODE_PERF2    = 4,
+
+	__SAM_PERF_MODE__START = 1,
+	__SAM_PERF_MODE__END   = 4,
+};
+
+enum sid_param_perf_mode {
+	SID_PARAM_PERF_MODE_AS_IS    = 0,
+	SID_PARAM_PERF_MODE_NORMAL   = SAM_PERF_MODE_NORMAL,
+	SID_PARAM_PERF_MODE_BATTERY  = SAM_PERF_MODE_BATTERY,
+	SID_PARAM_PERF_MODE_PERF1    = SAM_PERF_MODE_PERF1,
+	SID_PARAM_PERF_MODE_PERF2    = SAM_PERF_MODE_PERF2,
+
+	__SID_PARAM_PERF_MODE__START = 0,
+	__SID_PARAM_PERF_MODE__END   = 4,
+};
+
+struct spm_data {
+	struct ssam_controller *ctrl;
+};
+
+
+struct ssam_perf_info {
+	__le32 mode;
+	__le16 unknown1;
+	__le16 unknown2;
+} __packed;
+
+static SSAM_DEFINE_SYNC_REQUEST_R(ssam_tmp_perf_mode_get, struct ssam_perf_info, {
+	.target_category = SSAM_SSH_TC_TMP,
+	.command_id      = 0x02,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static SSAM_DEFINE_SYNC_REQUEST_W(__ssam_tmp_perf_mode_set, __le32, {
+	.target_category = SSAM_SSH_TC_TMP,
+	.command_id      = 0x03,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static int ssam_tmp_perf_mode_set(struct ssam_controller *ctrl, u32 mode)
+{
+	__le32 mode_le = cpu_to_le32(mode);
+
+	if (mode < __SAM_PERF_MODE__START || mode > __SAM_PERF_MODE__END)
+		return -EINVAL;
+
+	return __ssam_tmp_perf_mode_set(ctrl, &mode_le);
+}
+
+
+static int param_perf_mode_set(const char *val, const struct kernel_param *kp)
+{
+	int perf_mode;
+	int status;
+
+	status = kstrtoint(val, 0, &perf_mode);
+	if (status)
+		return status;
+
+	if (perf_mode < __SID_PARAM_PERF_MODE__START || perf_mode > __SID_PARAM_PERF_MODE__END)
+		return -EINVAL;
+
+	return param_set_int(val, kp);
+}
+
+static const struct kernel_param_ops param_perf_mode_ops = {
+	.set = param_perf_mode_set,
+	.get = param_get_int,
+};
+
+static int param_perf_mode_init = SID_PARAM_PERF_MODE_AS_IS;
+static int param_perf_mode_exit = SID_PARAM_PERF_MODE_AS_IS;
+
+module_param_cb(perf_mode_init, &param_perf_mode_ops, &param_perf_mode_init, SID_PARAM_PERM);
+module_param_cb(perf_mode_exit, &param_perf_mode_ops, &param_perf_mode_exit, SID_PARAM_PERM);
+
+MODULE_PARM_DESC(perf_mode_init, "Performance-mode to be set on module initialization");
+MODULE_PARM_DESC(perf_mode_exit, "Performance-mode to be set on module exit");
+
+
+static ssize_t perf_mode_show(struct device *dev, struct device_attribute *attr, char *data)
+{
+	struct spm_data *d = dev_get_drvdata(dev);
+	struct ssam_perf_info info;
+	int status;
+
+	status = ssam_tmp_perf_mode_get(d->ctrl, &info);
+	if (status) {
+		dev_err(dev, "failed to get current performance mode: %d\n", status);
+		return -EIO;
+	}
+
+	return sprintf(data, "%d\n", le32_to_cpu(info.mode));
+}
+
+static ssize_t perf_mode_store(struct device *dev, struct device_attribute *attr,
+			       const char *data, size_t count)
+{
+	struct spm_data *d = dev_get_drvdata(dev);
+	int perf_mode;
+	int status;
+
+	status = kstrtoint(data, 0, &perf_mode);
+	if (status)
+		return status;
+
+	status = ssam_tmp_perf_mode_set(d->ctrl, perf_mode);
+	if (status)
+		return status;
+
+	// TODO: Should we notify ACPI here?
+	//
+	//       There is a _DSM call described as
+	//           WSID._DSM: Notify DPTF on Slider State change
+	//       which calls
+	//           ODV3 = ToInteger (Arg3)
+	//           Notify(IETM, 0x88)
+	//       IETM is an INT3400 Intel Dynamic Power Performance Management
+	//       device, part of the DPTF framework. From the corresponding
+	//       kernel driver, it looks like event 0x88 is being ignored. Also
+	//       it is currently unknown what the consequecnes of setting ODV3
+	//       are.
+
+	return count;
+}
+
+static const DEVICE_ATTR_RW(perf_mode);
+
+
+static int surface_sam_sid_perfmode_probe(struct platform_device *pdev)
+{
+	struct ssam_controller *ctrl;
+	struct spm_data *data;
+	int status;
+
+	// link to ec
+	status = ssam_client_bind(&pdev->dev, &ctrl);
+	if (status)
+		return status == -ENXIO ? -EPROBE_DEFER : status;
+
+	data = devm_kzalloc(&pdev->dev, sizeof(struct spm_data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->ctrl = ctrl;
+	platform_set_drvdata(pdev, data);
+
+	// set initial perf_mode
+	if (param_perf_mode_init != SID_PARAM_PERF_MODE_AS_IS) {
+		status = ssam_tmp_perf_mode_set(ctrl, param_perf_mode_init);
+		if (status)
+			return status;
+	}
+
+	// register perf_mode attribute
+	status = sysfs_create_file(&pdev->dev.kobj, &dev_attr_perf_mode.attr);
+	if (status)
+		goto err_sysfs;
+
+	return 0;
+
+err_sysfs:
+	ssam_tmp_perf_mode_set(ctrl, param_perf_mode_exit);
+	return status;
+}
+
+static int surface_sam_sid_perfmode_remove(struct platform_device *pdev)
+{
+	struct spm_data *data = platform_get_drvdata(pdev);
+
+	sysfs_remove_file(&pdev->dev.kobj, &dev_attr_perf_mode.attr);
+	ssam_tmp_perf_mode_set(data->ctrl, param_perf_mode_exit);
+
+	platform_set_drvdata(pdev, NULL);
+	return 0;
+}
+
+static struct platform_driver surface_sam_sid_perfmode = {
+	.probe = surface_sam_sid_perfmode_probe,
+	.remove = surface_sam_sid_perfmode_remove,
+	.driver = {
+		.name = "surface_sam_sid_perfmode",
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+module_platform_driver(surface_sam_sid_perfmode);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("Surface Performance Mode Driver for 5th Generation Surface Devices");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:surface_sam_sid_perfmode");
diff --git a/drivers/platform/x86/surface_sam/surface_sam_sid_power.c b/drivers/platform/x86/surface_sam/surface_sam_sid_power.c
new file mode 100644
index 000000000000..64a3d46a128c
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_sid_power.c
@@ -0,0 +1,1054 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Surface SID Battery/AC Driver.
+ * Provides support for the battery and AC on 7th generation Surface devices.
+ */
+
+#include <asm/unaligned.h>
+#include <linux/kernel.h>
+#include <linux/delay.h>
+#include <linux/jiffies.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/power_supply.h>
+#include <linux/workqueue.h>
+
+#include "surface_sam_ssh.h"
+#include "surface_sam_sid_power.h"
+
+#define SPWR_WARN	KERN_WARNING KBUILD_MODNAME ": "
+#define SPWR_DEBUG	KERN_DEBUG KBUILD_MODNAME ": "
+
+
+// TODO: check BIX/BST for unknown/unsupported 0xffffffff entries
+// TODO: DPTF (/SAN notifications)?
+// TODO: other properties?
+
+
+static unsigned int cache_time = 1000;
+module_param(cache_time, uint, 0644);
+MODULE_PARM_DESC(cache_time, "battery state chaching time in milliseconds [default: 1000]");
+
+#define SPWR_AC_BAT_UPDATE_DELAY	msecs_to_jiffies(5000)
+
+
+/*
+ * SAM Interface.
+ */
+
+#define SAM_EVENT_PWR_CID_BIX		0x15
+#define SAM_EVENT_PWR_CID_BST		0x16
+#define SAM_EVENT_PWR_CID_ADAPTER	0x17
+
+#define SAM_BATTERY_STA_OK		0x0f
+#define SAM_BATTERY_STA_PRESENT		0x10
+
+#define SAM_BATTERY_STATE_DISCHARGING	0x01
+#define SAM_BATTERY_STATE_CHARGING	0x02
+#define SAM_BATTERY_STATE_CRITICAL	0x04
+
+#define SAM_BATTERY_POWER_UNIT_MA	1
+
+
+/* Equivalent to data returned in ACPI _BIX method */
+struct spwr_bix {
+	u8  revision;
+	__le32 power_unit;
+	__le32 design_cap;
+	__le32 last_full_charge_cap;
+	__le32 technology;
+	__le32 design_voltage;
+	__le32 design_cap_warn;
+	__le32 design_cap_low;
+	__le32 cycle_count;
+	__le32 measurement_accuracy;
+	__le32 max_sampling_time;
+	__le32 min_sampling_time;
+	__le32 max_avg_interval;
+	__le32 min_avg_interval;
+	__le32 bat_cap_granularity_1;
+	__le32 bat_cap_granularity_2;
+	u8  model[21];
+	u8  serial[11];
+	u8  type[5];
+	u8  oem_info[21];
+} __packed;
+
+/* Equivalent to data returned in ACPI _BST method */
+struct spwr_bst {
+	__le32 state;
+	__le32 present_rate;
+	__le32 remaining_cap;
+	__le32 present_voltage;
+} __packed;
+
+/* DPTF event payload */
+struct spwr_event_dptf {
+	__le32 pmax;
+	__le32 _1;		/* currently unknown */
+	__le32 _2;		/* currently unknown */
+} __packed;
+
+
+/* Get battery status (_STA) */
+static SSAM_DEFINE_SYNC_REQUEST_MD_R(ssam_bat_get_sta, __le32, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x01,
+});
+
+/* Get battery static information (_BIX) */
+static SSAM_DEFINE_SYNC_REQUEST_MD_R(ssam_bat_get_bix, struct spwr_bix, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x02,
+});
+
+/* Get battery dynamic information (_BST) */
+static SSAM_DEFINE_SYNC_REQUEST_MD_R(ssam_bat_get_bst, struct spwr_bst, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x03,
+});
+
+/* Set battery trip point (_BTP) */
+static SSAM_DEFINE_SYNC_REQUEST_MD_W(ssam_bat_set_btp, __le32, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x04,
+});
+
+/* Get platform power soruce for battery (DPTF PSRC) */
+static SSAM_DEFINE_SYNC_REQUEST_MD_R(ssam_bat_get_psrc, __le32, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x0d,
+});
+
+/* Get maximum platform power for battery (DPTF PMAX) */
+__always_unused
+static SSAM_DEFINE_SYNC_REQUEST_MD_R(ssam_bat_get_pmax, __le32, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x0b,
+});
+
+/* Get adapter rating (DPTF ARTG) */
+__always_unused
+static SSAM_DEFINE_SYNC_REQUEST_MD_R(ssam_bat_get_artg, __le32, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x0f,
+});
+
+/* Unknown (DPTF PSOC) */
+__always_unused
+static SSAM_DEFINE_SYNC_REQUEST_MD_R(ssam_bat_get_psoc, __le32, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x0c,
+});
+
+/* Unknown (DPTF CHGI/ INT3403 SPPC) */
+__always_unused
+static SSAM_DEFINE_SYNC_REQUEST_MD_W(ssam_bat_set_chgi, __le32, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x0e,
+});
+
+
+/*
+ * Common Power-Subsystem Interface.
+ */
+
+struct spwr_battery_device {
+	struct platform_device *pdev;
+	struct ssam_controller *ctrl;
+	const struct ssam_battery_properties *p;
+
+	char name[32];
+	struct power_supply *psy;
+	struct power_supply_desc psy_desc;
+
+	struct delayed_work update_work;
+
+	struct ssam_event_notifier notif;
+
+	struct mutex lock;
+	unsigned long timestamp;
+
+	__le32 sta;
+	struct spwr_bix bix;
+	struct spwr_bst bst;
+	u32 alarm;
+};
+
+struct spwr_ac_device {
+	struct platform_device *pdev;
+	struct ssam_controller *ctrl;
+
+	char name[32];
+	struct power_supply *psy;
+	struct power_supply_desc psy_desc;
+
+	struct ssam_event_notifier notif;
+
+	struct mutex lock;
+
+	__le32 state;
+};
+
+static enum power_supply_property spwr_ac_props[] = {
+	POWER_SUPPLY_PROP_ONLINE,
+};
+
+static enum power_supply_property spwr_battery_props_chg[] = {
+	POWER_SUPPLY_PROP_STATUS,
+	POWER_SUPPLY_PROP_PRESENT,
+	POWER_SUPPLY_PROP_TECHNOLOGY,
+	POWER_SUPPLY_PROP_CYCLE_COUNT,
+	POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN,
+	POWER_SUPPLY_PROP_VOLTAGE_NOW,
+	POWER_SUPPLY_PROP_CURRENT_NOW,
+	POWER_SUPPLY_PROP_CHARGE_FULL_DESIGN,
+	POWER_SUPPLY_PROP_CHARGE_FULL,
+	POWER_SUPPLY_PROP_CHARGE_NOW,
+	POWER_SUPPLY_PROP_CAPACITY,
+	POWER_SUPPLY_PROP_CAPACITY_LEVEL,
+	POWER_SUPPLY_PROP_MODEL_NAME,
+	POWER_SUPPLY_PROP_MANUFACTURER,
+	POWER_SUPPLY_PROP_SERIAL_NUMBER,
+};
+
+static enum power_supply_property spwr_battery_props_eng[] = {
+	POWER_SUPPLY_PROP_STATUS,
+	POWER_SUPPLY_PROP_PRESENT,
+	POWER_SUPPLY_PROP_TECHNOLOGY,
+	POWER_SUPPLY_PROP_CYCLE_COUNT,
+	POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN,
+	POWER_SUPPLY_PROP_VOLTAGE_NOW,
+	POWER_SUPPLY_PROP_POWER_NOW,
+	POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN,
+	POWER_SUPPLY_PROP_ENERGY_FULL,
+	POWER_SUPPLY_PROP_ENERGY_NOW,
+	POWER_SUPPLY_PROP_CAPACITY,
+	POWER_SUPPLY_PROP_CAPACITY_LEVEL,
+	POWER_SUPPLY_PROP_MODEL_NAME,
+	POWER_SUPPLY_PROP_MANUFACTURER,
+	POWER_SUPPLY_PROP_SERIAL_NUMBER,
+};
+
+
+static int spwr_battery_register(struct spwr_battery_device *bat,
+				 struct platform_device *pdev,
+				 struct ssam_controller *ctrl,
+				 const struct ssam_battery_properties *p);
+
+static void spwr_battery_unregister(struct spwr_battery_device *bat);
+
+
+static inline bool spwr_battery_present(struct spwr_battery_device *bat)
+{
+	return le32_to_cpu(bat->sta) & SAM_BATTERY_STA_PRESENT;
+}
+
+
+static inline int spwr_battery_load_sta(struct spwr_battery_device *bat)
+{
+	return ssam_bat_get_sta(bat->ctrl, bat->p->channel, bat->p->instance,
+				&bat->sta);
+}
+
+static inline int spwr_battery_load_bix(struct spwr_battery_device *bat)
+{
+	if (!spwr_battery_present(bat))
+		return 0;
+
+	return ssam_bat_get_bix(bat->ctrl, bat->p->channel, bat->p->instance,
+				&bat->bix);
+}
+
+static inline int spwr_battery_load_bst(struct spwr_battery_device *bat)
+{
+	if (!spwr_battery_present(bat))
+		return 0;
+
+	return ssam_bat_get_bst(bat->ctrl, bat->p->channel, bat->p->instance,
+				&bat->bst);
+}
+
+
+static inline int spwr_battery_set_alarm_unlocked(struct spwr_battery_device *bat, u32 value)
+{
+	__le32 alarm = cpu_to_le32(value);
+
+	bat->alarm = value;
+	return ssam_bat_set_btp(bat->ctrl, bat->p->channel, bat->p->instance,
+				&alarm);
+}
+
+static inline int spwr_battery_set_alarm(struct spwr_battery_device *bat, u32 value)
+{
+	int status;
+
+	mutex_lock(&bat->lock);
+	status = spwr_battery_set_alarm_unlocked(bat, value);
+	mutex_unlock(&bat->lock);
+
+	return status;
+}
+
+static inline int spwr_battery_update_bst_unlocked(struct spwr_battery_device *bat, bool cached)
+{
+	unsigned long cache_deadline = bat->timestamp + msecs_to_jiffies(cache_time);
+	int status;
+
+	if (cached && bat->timestamp && time_is_after_jiffies(cache_deadline))
+		return 0;
+
+	status = spwr_battery_load_sta(bat);
+	if (status)
+		return status;
+
+	status = spwr_battery_load_bst(bat);
+	if (status)
+		return status;
+
+	bat->timestamp = jiffies;
+	return 0;
+}
+
+static int spwr_battery_update_bst(struct spwr_battery_device *bat, bool cached)
+{
+	int status;
+
+	mutex_lock(&bat->lock);
+	status = spwr_battery_update_bst_unlocked(bat, cached);
+	mutex_unlock(&bat->lock);
+
+	return status;
+}
+
+static inline int spwr_battery_update_bix_unlocked(struct spwr_battery_device *bat)
+{
+	int status;
+
+	status = spwr_battery_load_sta(bat);
+	if (status)
+		return status;
+
+	status = spwr_battery_load_bix(bat);
+	if (status)
+		return status;
+
+	status = spwr_battery_load_bst(bat);
+	if (status)
+		return status;
+
+	bat->timestamp = jiffies;
+	return 0;
+}
+
+static int spwr_battery_update_bix(struct spwr_battery_device *bat)
+{
+	int status;
+
+	mutex_lock(&bat->lock);
+	status = spwr_battery_update_bix_unlocked(bat);
+	mutex_unlock(&bat->lock);
+
+	return status;
+}
+
+static inline int spwr_ac_update_unlocked(struct spwr_ac_device *ac)
+{
+	return ssam_bat_get_psrc(ac->ctrl, 0x01, 0x01, &ac->state);
+}
+
+static int spwr_ac_update(struct spwr_ac_device *ac)
+{
+	int status;
+
+	mutex_lock(&ac->lock);
+	status = spwr_ac_update_unlocked(ac);
+	mutex_unlock(&ac->lock);
+
+	return status;
+}
+
+
+static int spwr_battery_recheck(struct spwr_battery_device *bat)
+{
+	bool present = spwr_battery_present(bat);
+	u32 unit = get_unaligned_le32(&bat->bix.power_unit);
+	int status;
+
+	status = spwr_battery_update_bix(bat);
+	if (status)
+		return status;
+
+	// if battery has been attached, (re-)initialize alarm
+	if (!present && spwr_battery_present(bat)) {
+		u32 cap_warn = get_unaligned_le32(&bat->bix.design_cap_warn);
+		status = spwr_battery_set_alarm(bat, cap_warn);
+		if (status)
+			return status;
+	}
+
+	// if the unit has changed, re-add the battery
+	if (unit != get_unaligned_le32(&bat->bix.power_unit)) {
+		spwr_battery_unregister(bat);
+		status = spwr_battery_register(bat, bat->pdev, bat->ctrl, bat->p);
+	}
+
+	return status;
+}
+
+
+static inline int spwr_notify_bix(struct spwr_battery_device *bat)
+{
+	int status;
+
+	status = spwr_battery_recheck(bat);
+	if (!status)
+		power_supply_changed(bat->psy);
+
+	return status;
+}
+
+static inline int spwr_notify_bst(struct spwr_battery_device *bat)
+{
+	int status;
+
+	status = spwr_battery_update_bst(bat, false);
+	if (!status)
+		power_supply_changed(bat->psy);
+
+	return status;
+}
+
+static inline int spwr_notify_adapter_bat(struct spwr_battery_device *bat)
+{
+	u32 last_full_cap = get_unaligned_le32(&bat->bix.last_full_charge_cap);
+	u32 remaining_cap = get_unaligned_le32(&bat->bst.remaining_cap);
+
+	/*
+	 * Handle battery update quirk:
+	 * When the battery is fully charged and the adapter is plugged in or
+	 * removed, the EC does not send a separate event for the state
+	 * (charging/discharging) change. Furthermore it may take some time until
+	 * the state is updated on the battery. Schedule an update to solve this.
+	 */
+
+	if (remaining_cap >= last_full_cap)
+		schedule_delayed_work(&bat->update_work, SPWR_AC_BAT_UPDATE_DELAY);
+
+	return 0;
+}
+
+static inline int spwr_notify_adapter_ac(struct spwr_ac_device *ac)
+{
+	int status;
+
+	status = spwr_ac_update(ac);
+	if (!status)
+		power_supply_changed(ac->psy);
+
+	return status;
+}
+
+static u32 spwr_notify_bat(struct ssam_notifier_block *nb, const struct ssam_event *event)
+{
+	struct spwr_battery_device *bat = container_of(nb, struct spwr_battery_device, notif.base);
+	int status;
+
+	dev_dbg(&bat->pdev->dev, "power event (cid = 0x%02x, iid = %d, chn = %d)\n",
+		event->command_id, event->instance_id, event->channel);
+
+	// handled here, needs to be handled for all channels/instances
+	if (event->command_id == SAM_EVENT_PWR_CID_ADAPTER) {
+		status = spwr_notify_adapter_bat(bat);
+		return ssam_notifier_from_errno(status) | SSAM_NOTIF_HANDLED;
+	}
+
+	// check for the correct channel and instance ID
+	if (event->channel != bat->p->channel)
+		return 0;
+
+	if (event->instance_id != bat->p->instance)
+		return 0;
+
+	switch (event->command_id) {
+	case SAM_EVENT_PWR_CID_BIX:
+		status = spwr_notify_bix(bat);
+		break;
+
+	case SAM_EVENT_PWR_CID_BST:
+		status = spwr_notify_bst(bat);
+		break;
+
+	default:
+		return 0;
+	}
+
+	return ssam_notifier_from_errno(status) | SSAM_NOTIF_HANDLED;
+}
+
+static u32 spwr_notify_ac(struct ssam_notifier_block *nb, const struct ssam_event *event)
+{
+	struct spwr_ac_device *ac = container_of(nb, struct spwr_ac_device, notif.base);
+	int status;
+
+	dev_dbg(&ac->pdev->dev, "power event (cid = 0x%02x, iid = %d, chn = %d)\n",
+		event->command_id, event->instance_id, event->channel);
+
+	// AC has IID = 0
+	if (event->instance_id != 0)
+		return 0;
+
+	switch (event->command_id) {
+	case SAM_EVENT_PWR_CID_ADAPTER:
+		status = spwr_notify_adapter_ac(ac);
+		return ssam_notifier_from_errno(status) | SSAM_NOTIF_HANDLED;
+
+	default:
+		return 0;
+	}
+}
+
+static void spwr_battery_update_bst_workfn(struct work_struct *work)
+{
+	struct delayed_work *dwork = to_delayed_work(work);
+	struct spwr_battery_device *bat = container_of(dwork, struct spwr_battery_device, update_work);
+	int status;
+
+	status = spwr_battery_update_bst(bat, false);
+	if (!status)
+		power_supply_changed(bat->psy);
+
+	if (status)
+		dev_err(&bat->pdev->dev, "failed to update battery state: %d\n", status);
+}
+
+
+static inline int spwr_battery_prop_status(struct spwr_battery_device *bat)
+{
+	u32 state = get_unaligned_le32(&bat->bst.state);
+	u32 last_full_cap = get_unaligned_le32(&bat->bix.last_full_charge_cap);
+	u32 remaining_cap = get_unaligned_le32(&bat->bst.remaining_cap);
+	u32 present_rate = get_unaligned_le32(&bat->bst.present_rate);
+
+	if (state & SAM_BATTERY_STATE_DISCHARGING)
+		return POWER_SUPPLY_STATUS_DISCHARGING;
+
+	if (state & SAM_BATTERY_STATE_CHARGING)
+		return POWER_SUPPLY_STATUS_CHARGING;
+
+	if (last_full_cap == remaining_cap)
+		return POWER_SUPPLY_STATUS_FULL;
+
+	if (present_rate == 0)
+		return POWER_SUPPLY_STATUS_NOT_CHARGING;
+
+	return POWER_SUPPLY_STATUS_UNKNOWN;
+}
+
+static inline int spwr_battery_prop_technology(struct spwr_battery_device *bat)
+{
+	if (!strcasecmp("NiCd", bat->bix.type))
+		return POWER_SUPPLY_TECHNOLOGY_NiCd;
+
+	if (!strcasecmp("NiMH", bat->bix.type))
+		return POWER_SUPPLY_TECHNOLOGY_NiMH;
+
+	if (!strcasecmp("LION", bat->bix.type))
+		return POWER_SUPPLY_TECHNOLOGY_LION;
+
+	if (!strncasecmp("LI-ION", bat->bix.type, 6))
+		return POWER_SUPPLY_TECHNOLOGY_LION;
+
+	if (!strcasecmp("LiP", bat->bix.type))
+		return POWER_SUPPLY_TECHNOLOGY_LIPO;
+
+	return POWER_SUPPLY_TECHNOLOGY_UNKNOWN;
+}
+
+static inline int spwr_battery_prop_capacity(struct spwr_battery_device *bat)
+{
+	u32 last_full_cap = get_unaligned_le32(&bat->bix.last_full_charge_cap);
+	u32 remaining_cap = get_unaligned_le32(&bat->bst.remaining_cap);
+
+	if (remaining_cap && last_full_cap)
+		return remaining_cap * 100 / last_full_cap;
+	else
+		return 0;
+}
+
+static inline int spwr_battery_prop_capacity_level(struct spwr_battery_device *bat)
+{
+	u32 state = get_unaligned_le32(&bat->bst.state);
+	u32 last_full_cap = get_unaligned_le32(&bat->bix.last_full_charge_cap);
+	u32 remaining_cap = get_unaligned_le32(&bat->bst.remaining_cap);
+
+	if (state & SAM_BATTERY_STATE_CRITICAL)
+		return POWER_SUPPLY_CAPACITY_LEVEL_CRITICAL;
+
+	if (remaining_cap >= last_full_cap)
+		return POWER_SUPPLY_CAPACITY_LEVEL_FULL;
+
+	if (remaining_cap <= bat->alarm)
+		return POWER_SUPPLY_CAPACITY_LEVEL_LOW;
+
+	return POWER_SUPPLY_CAPACITY_LEVEL_NORMAL;
+}
+
+static int spwr_ac_get_property(struct power_supply *psy,
+				enum power_supply_property psp,
+				union power_supply_propval *val)
+{
+	struct spwr_ac_device *ac = power_supply_get_drvdata(psy);
+	int status;
+
+	mutex_lock(&ac->lock);
+
+	status = spwr_ac_update_unlocked(ac);
+	if (status)
+		goto out;
+
+	switch (psp) {
+	case POWER_SUPPLY_PROP_ONLINE:
+		val->intval = le32_to_cpu(ac->state) == 1;
+		break;
+
+	default:
+		status = -EINVAL;
+		goto out;
+	}
+
+out:
+	mutex_unlock(&ac->lock);
+	return status;
+}
+
+static int spwr_battery_get_property(struct power_supply *psy,
+				     enum power_supply_property psp,
+				     union power_supply_propval *val)
+{
+	struct spwr_battery_device *bat = power_supply_get_drvdata(psy);
+	int status;
+
+	mutex_lock(&bat->lock);
+
+	status = spwr_battery_update_bst_unlocked(bat, true);
+	if (status)
+		goto out;
+
+	// abort if battery is not present
+	if (!spwr_battery_present(bat) && psp != POWER_SUPPLY_PROP_PRESENT) {
+		status = -ENODEV;
+		goto out;
+	}
+
+	switch (psp) {
+	case POWER_SUPPLY_PROP_STATUS:
+		val->intval = spwr_battery_prop_status(bat);
+		break;
+
+	case POWER_SUPPLY_PROP_PRESENT:
+		val->intval = spwr_battery_present(bat);
+		break;
+
+	case POWER_SUPPLY_PROP_TECHNOLOGY:
+		val->intval = spwr_battery_prop_technology(bat);
+		break;
+
+	case POWER_SUPPLY_PROP_CYCLE_COUNT:
+		val->intval = get_unaligned_le32(&bat->bix.cycle_count);
+		break;
+
+	case POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN:
+		val->intval = get_unaligned_le32(&bat->bix.design_voltage)
+			      * 1000;
+		break;
+
+	case POWER_SUPPLY_PROP_VOLTAGE_NOW:
+		val->intval = get_unaligned_le32(&bat->bst.present_voltage)
+			      * 1000;
+		break;
+
+	case POWER_SUPPLY_PROP_CURRENT_NOW:
+	case POWER_SUPPLY_PROP_POWER_NOW:
+		val->intval = get_unaligned_le32(&bat->bst.present_rate) * 1000;
+		break;
+
+	case POWER_SUPPLY_PROP_CHARGE_FULL_DESIGN:
+	case POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN:
+		val->intval = get_unaligned_le32(&bat->bix.design_cap) * 1000;
+		break;
+
+	case POWER_SUPPLY_PROP_CHARGE_FULL:
+	case POWER_SUPPLY_PROP_ENERGY_FULL:
+		val->intval = get_unaligned_le32(&bat->bix.last_full_charge_cap)
+			      * 1000;
+		break;
+
+	case POWER_SUPPLY_PROP_CHARGE_NOW:
+	case POWER_SUPPLY_PROP_ENERGY_NOW:
+		val->intval = get_unaligned_le32(&bat->bst.remaining_cap)
+			      * 1000;
+		break;
+
+	case POWER_SUPPLY_PROP_CAPACITY:
+		val->intval = spwr_battery_prop_capacity(bat);
+		break;
+
+	case POWER_SUPPLY_PROP_CAPACITY_LEVEL:
+		val->intval = spwr_battery_prop_capacity_level(bat);
+		break;
+
+	case POWER_SUPPLY_PROP_MODEL_NAME:
+		val->strval = bat->bix.model;
+		break;
+
+	case POWER_SUPPLY_PROP_MANUFACTURER:
+		val->strval = bat->bix.oem_info;
+		break;
+
+	case POWER_SUPPLY_PROP_SERIAL_NUMBER:
+		val->strval = bat->bix.serial;
+		break;
+
+	default:
+		status = -EINVAL;
+		goto out;
+	}
+
+out:
+	mutex_unlock(&bat->lock);
+	return status;
+}
+
+
+static ssize_t spwr_battery_alarm_show(struct device *dev,
+				       struct device_attribute *attr,
+				       char *buf)
+{
+	struct power_supply *psy = dev_get_drvdata(dev);
+	struct spwr_battery_device *bat = power_supply_get_drvdata(psy);
+
+	return sprintf(buf, "%d\n", bat->alarm * 1000);
+}
+
+static ssize_t spwr_battery_alarm_store(struct device *dev,
+					struct device_attribute *attr,
+					const char *buf, size_t count)
+{
+	struct power_supply *psy = dev_get_drvdata(dev);
+	struct spwr_battery_device *bat = power_supply_get_drvdata(psy);
+	unsigned long value;
+	int status;
+
+	status = kstrtoul(buf, 0, &value);
+	if (status)
+		return status;
+
+	if (!spwr_battery_present(bat))
+		return -ENODEV;
+
+	status = spwr_battery_set_alarm(bat, value / 1000);
+	if (status)
+		return status;
+
+	return count;
+}
+
+static const struct device_attribute alarm_attr = {
+	.attr = {.name = "alarm", .mode = 0644},
+	.show = spwr_battery_alarm_show,
+	.store = spwr_battery_alarm_store,
+};
+
+
+static int spwr_ac_register(struct spwr_ac_device *ac,
+			    struct platform_device *pdev,
+			    struct ssam_controller *ctrl)
+{
+	struct power_supply_config psy_cfg = {};
+	__le32 sta;
+	int status;
+
+	// make sure the device is there and functioning properly
+	status = ssam_bat_get_sta(ctrl, 0x01, 0x01, &sta);
+	if (status)
+		return status;
+
+	if ((le32_to_cpu(sta) & SAM_BATTERY_STA_OK) != SAM_BATTERY_STA_OK)
+		return -ENODEV;
+
+	psy_cfg.drv_data = ac;
+
+	ac->pdev = pdev;
+	ac->ctrl = ctrl;
+	mutex_init(&ac->lock);
+
+	snprintf(ac->name, ARRAY_SIZE(ac->name), "ADP0");
+
+	ac->psy_desc.name = ac->name;
+	ac->psy_desc.type = POWER_SUPPLY_TYPE_MAINS;
+	ac->psy_desc.properties = spwr_ac_props;
+	ac->psy_desc.num_properties = ARRAY_SIZE(spwr_ac_props);
+	ac->psy_desc.get_property = spwr_ac_get_property;
+
+	ac->psy = power_supply_register(&ac->pdev->dev, &ac->psy_desc, &psy_cfg);
+	if (IS_ERR(ac->psy)) {
+		status = PTR_ERR(ac->psy);
+		goto err_psy;
+	}
+
+	ac->notif.base.priority = 1;
+	ac->notif.base.fn = spwr_notify_ac;
+	ac->notif.event.reg = SSAM_EVENT_REGISTRY_SAM;
+	ac->notif.event.id.target_category = SSAM_SSH_TC_BAT;
+	ac->notif.event.id.instance = 0;
+	ac->notif.event.flags = SSAM_EVENT_SEQUENCED;
+
+	status = ssam_notifier_register(ctrl, &ac->notif);
+	if (status)
+		goto err_notif;
+
+	return 0;
+
+err_notif:
+	power_supply_unregister(ac->psy);
+err_psy:
+	mutex_destroy(&ac->lock);
+	return status;
+}
+
+static int spwr_ac_unregister(struct spwr_ac_device *ac)
+{
+	ssam_notifier_unregister(ac->ctrl, &ac->notif);
+	power_supply_unregister(ac->psy);
+	mutex_destroy(&ac->lock);
+	return 0;
+}
+
+static int spwr_battery_register(struct spwr_battery_device *bat,
+				 struct platform_device *pdev,
+				 struct ssam_controller *ctrl,
+				 const struct ssam_battery_properties *p)
+{
+	struct power_supply_config psy_cfg = {};
+	__le32 sta;
+	int status;
+
+	bat->pdev = pdev;
+	bat->ctrl = ctrl;
+	bat->p = p;
+
+	// make sure the device is there and functioning properly
+	status = ssam_bat_get_sta(ctrl, bat->p->channel, bat->p->instance, &sta);
+	if (status)
+		return status;
+
+	if ((le32_to_cpu(sta) & SAM_BATTERY_STA_OK) != SAM_BATTERY_STA_OK)
+		return -ENODEV;
+
+	status = spwr_battery_update_bix_unlocked(bat);
+	if (status)
+		return status;
+
+	if (spwr_battery_present(bat)) {
+		u32 cap_warn = get_unaligned_le32(&bat->bix.design_cap_warn);
+		status = spwr_battery_set_alarm_unlocked(bat, cap_warn);
+		if (status)
+			return status;
+	}
+
+	snprintf(bat->name, ARRAY_SIZE(bat->name), "BAT%d", bat->p->num);
+	bat->psy_desc.name = bat->name;
+	bat->psy_desc.type = POWER_SUPPLY_TYPE_BATTERY;
+
+	if (get_unaligned_le32(&bat->bix.power_unit) == SAM_BATTERY_POWER_UNIT_MA) {
+		bat->psy_desc.properties = spwr_battery_props_chg;
+		bat->psy_desc.num_properties = ARRAY_SIZE(spwr_battery_props_chg);
+	} else {
+		bat->psy_desc.properties = spwr_battery_props_eng;
+		bat->psy_desc.num_properties = ARRAY_SIZE(spwr_battery_props_eng);
+	}
+
+	bat->psy_desc.get_property = spwr_battery_get_property;
+
+	mutex_init(&bat->lock);
+	psy_cfg.drv_data = bat;
+
+	INIT_DELAYED_WORK(&bat->update_work, spwr_battery_update_bst_workfn);
+
+	bat->psy = power_supply_register(&bat->pdev->dev, &bat->psy_desc, &psy_cfg);
+	if (IS_ERR(bat->psy)) {
+		status = PTR_ERR(bat->psy);
+		goto err_psy;
+	}
+
+	bat->notif.base.priority = 1;
+	bat->notif.base.fn = spwr_notify_bat;
+	bat->notif.event.reg = p->registry;
+	bat->notif.event.id.target_category = SSAM_SSH_TC_BAT;
+	bat->notif.event.id.instance = 0;
+	bat->notif.event.flags = SSAM_EVENT_SEQUENCED;
+
+	status = ssam_notifier_register(ctrl, &bat->notif);
+	if (status)
+		goto err_notif;
+
+	status = device_create_file(&bat->psy->dev, &alarm_attr);
+	if (status)
+		goto err_file;
+
+	return 0;
+
+err_file:
+	ssam_notifier_unregister(ctrl, &bat->notif);
+err_notif:
+	power_supply_unregister(bat->psy);
+err_psy:
+	mutex_destroy(&bat->lock);
+	return status;
+}
+
+static void spwr_battery_unregister(struct spwr_battery_device *bat)
+{
+	ssam_notifier_unregister(bat->ctrl, &bat->notif);
+	cancel_delayed_work_sync(&bat->update_work);
+	device_remove_file(&bat->psy->dev, &alarm_attr);
+	power_supply_unregister(bat->psy);
+	mutex_destroy(&bat->lock);
+}
+
+
+/*
+ * Battery Driver.
+ */
+
+#ifdef CONFIG_PM_SLEEP
+static int surface_sam_sid_battery_resume(struct device *dev)
+{
+	struct spwr_battery_device *bat;
+
+	bat = dev_get_drvdata(dev);
+	return spwr_battery_recheck(bat);
+}
+#else
+#define surface_sam_sid_battery_resume NULL
+#endif
+
+SIMPLE_DEV_PM_OPS(surface_sam_sid_battery_pm, NULL, surface_sam_sid_battery_resume);
+
+static int surface_sam_sid_battery_probe(struct platform_device *pdev)
+{
+	struct spwr_battery_device *bat;
+	struct ssam_controller *ctrl;
+	int status;
+
+	// link to ec
+	status = ssam_client_bind(&pdev->dev, &ctrl);
+	if (status)
+		return status == -ENXIO ? -EPROBE_DEFER : status;
+
+	bat = devm_kzalloc(&pdev->dev, sizeof(struct spwr_battery_device), GFP_KERNEL);
+	if (!bat)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, bat);
+	return spwr_battery_register(bat, pdev, ctrl, pdev->dev.platform_data);
+}
+
+static int surface_sam_sid_battery_remove(struct platform_device *pdev)
+{
+	struct spwr_battery_device *bat;
+
+	bat = platform_get_drvdata(pdev);
+	spwr_battery_unregister(bat);
+
+	return 0;
+}
+
+static struct platform_driver surface_sam_sid_battery = {
+	.probe = surface_sam_sid_battery_probe,
+	.remove = surface_sam_sid_battery_remove,
+	.driver = {
+		.name = "surface_sam_sid_battery",
+		.pm = &surface_sam_sid_battery_pm,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+
+
+/*
+ * AC Driver.
+ */
+
+static int surface_sam_sid_ac_probe(struct platform_device *pdev)
+{
+	struct spwr_ac_device *ac;
+	struct ssam_controller *ctrl;
+	int status;
+
+	// link to ec
+	status = ssam_client_bind(&pdev->dev, &ctrl);
+	if (status)
+		return status == -ENXIO ? -EPROBE_DEFER : status;
+
+	ac = devm_kzalloc(&pdev->dev, sizeof(struct spwr_ac_device), GFP_KERNEL);
+	if (!ac)
+		return -ENOMEM;
+
+	status = spwr_ac_register(ac, pdev, ctrl);
+	if (status)
+		return status;
+
+	platform_set_drvdata(pdev, ac);
+	return 0;
+}
+
+static int surface_sam_sid_ac_remove(struct platform_device *pdev)
+{
+	struct spwr_ac_device *ac;
+
+	ac = platform_get_drvdata(pdev);
+	return spwr_ac_unregister(ac);
+}
+
+static struct platform_driver surface_sam_sid_ac = {
+	.probe = surface_sam_sid_ac_probe,
+	.remove = surface_sam_sid_ac_remove,
+	.driver = {
+		.name = "surface_sam_sid_ac",
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+
+
+static int __init surface_sam_sid_power_init(void)
+{
+	int status;
+
+	status = platform_driver_register(&surface_sam_sid_battery);
+	if (status)
+		return status;
+
+	status = platform_driver_register(&surface_sam_sid_ac);
+	if (status) {
+		platform_driver_unregister(&surface_sam_sid_battery);
+		return status;
+	}
+
+	return 0;
+}
+
+static void __exit surface_sam_sid_power_exit(void)
+{
+	platform_driver_unregister(&surface_sam_sid_battery);
+	platform_driver_unregister(&surface_sam_sid_ac);
+}
+
+module_init(surface_sam_sid_power_init);
+module_exit(surface_sam_sid_power_exit);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("Surface Battery/AC Driver for 7th Generation Surface Devices");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:surface_sam_sid_ac");
+MODULE_ALIAS("platform:surface_sam_sid_battery");
diff --git a/drivers/platform/x86/surface_sam/surface_sam_sid_power.h b/drivers/platform/x86/surface_sam/surface_sam_sid_power.h
new file mode 100644
index 000000000000..d8d9509b7d12
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_sid_power.h
@@ -0,0 +1,16 @@
+
+#ifndef _SURFACE_SAM_SID_POWER_H
+#define _SURFACE_SAM_SID_POWER_H
+
+#include <linux/types.h>
+#include "surface_sam_ssh.h"
+
+
+struct ssam_battery_properties {
+	struct ssam_event_registry registry;
+	u8 num;
+	u8 channel;
+	u8 instance;
+};
+
+#endif /* _SURFACE_SAM_SID_POWER_H */
diff --git a/drivers/platform/x86/surface_sam/surface_sam_sid_vhf.c b/drivers/platform/x86/surface_sam/surface_sam_sid_vhf.c
new file mode 100644
index 000000000000..a6059d679661
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_sid_vhf.c
@@ -0,0 +1,429 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Microsofs Surface HID (VHF) driver for HID input events via SAM.
+ * Used for keyboard input events on the 7th generation Surface Laptops.
+ */
+
+#include <linux/acpi.h>
+#include <linux/hid.h>
+#include <linux/input.h>
+#include <linux/platform_device.h>
+#include <linux/types.h>
+
+#include "surface_sam_ssh.h"
+#include "surface_sam_sid_vhf.h"
+
+#define SID_VHF_INPUT_NAME	"Microsoft Surface HID"
+
+#define SAM_EVENT_SID_VHF_TC	0x15
+
+#define VHF_HID_STARTED		0
+
+struct sid_vhf {
+	struct platform_device *dev;
+	struct ssam_controller *ctrl;
+	const struct ssam_hid_properties *p;
+
+	struct ssam_event_notifier notif;
+
+	struct hid_device *hid;
+	unsigned long state;
+};
+
+
+static int sid_vhf_hid_start(struct hid_device *hid)
+{
+	hid_dbg(hid, "%s\n", __func__);
+	return 0;
+}
+
+static void sid_vhf_hid_stop(struct hid_device *hid)
+{
+	hid_dbg(hid, "%s\n", __func__);
+}
+
+static int sid_vhf_hid_open(struct hid_device *hid)
+{
+	struct sid_vhf *vhf = dev_get_drvdata(hid->dev.parent);
+
+	hid_dbg(hid, "%s\n", __func__);
+
+	set_bit(VHF_HID_STARTED, &vhf->state);
+	return 0;
+}
+
+static void sid_vhf_hid_close(struct hid_device *hid)
+{
+
+	struct sid_vhf *vhf = dev_get_drvdata(hid->dev.parent);
+
+	hid_dbg(hid, "%s\n", __func__);
+
+	clear_bit(VHF_HID_STARTED, &vhf->state);
+}
+
+struct surface_sam_sid_vhf_meta_rqst {
+	u8 id;
+	u32 offset;
+	u32 length; // buffer limit on send, length of data received on receive
+	u8 end; // 0x01 if end was reached
+} __packed;
+
+struct vhf_device_metadata_info {
+	u8 len;
+	u8 _2;
+	u8 _3;
+	u8 _4;
+	u8 _5;
+	u8 _6;
+	u8 _7;
+	u16 hid_len; // hid descriptor length
+} __packed;
+
+struct vhf_device_metadata {
+	u32 len;
+	u16 vendor_id;
+	u16 product_id;
+	u8  _1[24];
+} __packed;
+
+union vhf_buffer_data {
+	struct vhf_device_metadata_info info;
+	u8 pld[0x76];
+	struct vhf_device_metadata meta;
+};
+
+struct surface_sam_sid_vhf_meta_resp {
+	struct surface_sam_sid_vhf_meta_rqst rqst;
+	union vhf_buffer_data data;
+} __packed;
+
+
+static int vhf_get_metadata(struct ssam_controller *ctrl, u8 iid,
+			    struct vhf_device_metadata *meta)
+{
+	struct surface_sam_sid_vhf_meta_resp data = {};
+	struct ssam_request rqst;
+	struct ssam_response rsp;
+	int status;
+
+	data.rqst.id = 2;
+	data.rqst.offset = 0;
+	data.rqst.length = 0x76;
+	data.rqst.end = 0;
+
+	rqst.target_category = SSAM_SSH_TC_HID;;
+	rqst.command_id = 0x04;
+	rqst.instance_id = iid;
+	rqst.channel = 0x02;
+	rqst.flags = SSAM_REQUEST_HAS_RESPONSE;
+	rqst.length = sizeof(struct surface_sam_sid_vhf_meta_rqst);
+	rqst.payload = (u8 *)&data.rqst;
+
+	rsp.capacity = sizeof(struct surface_sam_sid_vhf_meta_resp);
+	rsp.length = 0;
+	rsp.pointer = (u8 *)&data;
+
+	status = ssam_request_sync(ctrl, &rqst, &rsp);
+	if (status)
+		return status;
+
+	*meta = data.data.meta;
+
+	return 0;
+}
+
+static int vhf_get_hid_descriptor(struct hid_device *hid, u8 iid, u8 **desc, int *size)
+{
+	struct sid_vhf *vhf = dev_get_drvdata(hid->dev.parent);
+	struct surface_sam_sid_vhf_meta_resp data = {};
+	struct ssam_request rqst;
+	struct ssam_response rsp;
+	int status, len;
+	u8 *buf;
+
+	data.rqst.id = 0;
+	data.rqst.offset = 0;
+	data.rqst.length = 0x76;
+	data.rqst.end = 0;
+
+	rqst.target_category = SSAM_SSH_TC_HID;
+	rqst.command_id = 0x04;
+	rqst.instance_id = iid;
+	rqst.channel = 0x02;
+	rqst.flags = SSAM_REQUEST_HAS_RESPONSE;
+	rqst.length = sizeof(struct surface_sam_sid_vhf_meta_rqst);
+	rqst.payload = (u8 *)&data.rqst;
+
+	rsp.capacity = sizeof(struct surface_sam_sid_vhf_meta_resp);
+	rsp.length = 0;
+	rsp.pointer = (u8 *)&data;
+
+	// first fetch 00 to get the total length
+	status = ssam_request_sync(vhf->ctrl, &rqst, &rsp);
+	if (status)
+		return status;
+
+	len = data.data.info.hid_len;
+
+	// allocate a buffer for the descriptor
+	buf = kzalloc(len, GFP_KERNEL);
+
+	// then, iterate and write into buffer, copying out bytes
+	data.rqst.id = 1;
+	data.rqst.offset = 0;
+	data.rqst.length = 0x76;
+	data.rqst.end = 0;
+
+	while (!data.rqst.end && data.rqst.offset < len) {
+		status = ssam_request_sync(vhf->ctrl, &rqst, &rsp);
+		if (status) {
+			kfree(buf);
+			return status;
+		}
+		memcpy(buf + data.rqst.offset, data.data.pld, data.rqst.length);
+
+		data.rqst.offset += data.rqst.length;
+	}
+
+	*desc = buf;
+	*size = len;
+
+	return 0;
+}
+
+static int sid_vhf_hid_parse(struct hid_device *hid)
+{
+	struct sid_vhf *vhf = dev_get_drvdata(hid->dev.parent);
+	int ret = 0, size;
+	u8 *buf;
+
+	ret = vhf_get_hid_descriptor(hid, vhf->p->instance, &buf, &size);
+	if (ret != 0) {
+		hid_err(hid, "Failed to read HID descriptor from device: %d\n", ret);
+		return -EIO;
+	}
+	hid_dbg(hid, "HID descriptor of device:");
+	print_hex_dump_debug("descriptor:", DUMP_PREFIX_OFFSET, 16, 1, buf, size, false);
+
+	ret = hid_parse_report(hid, buf, size);
+	kfree(buf);
+	return ret;
+
+}
+
+static int sid_vhf_hid_raw_request(struct hid_device *hid, unsigned char
+		reportnum, u8 *buf, size_t len, unsigned char rtype, int
+		reqtype)
+{
+	struct sid_vhf *vhf = dev_get_drvdata(hid->dev.parent);
+	struct ssam_request rqst;
+	struct ssam_response rsp;
+	int status;
+	u8 cid;
+
+	hid_dbg(hid, "%s: reportnum=%#04x rtype=%i reqtype=%i\n", __func__, reportnum, rtype, reqtype);
+	print_hex_dump_debug("report:", DUMP_PREFIX_OFFSET, 16, 1, buf, len, false);
+
+	// Byte 0 is the report number. Report data starts at byte 1.
+	buf[0] = reportnum;
+
+	switch (rtype) {
+	case HID_OUTPUT_REPORT:
+		cid = 0x01;
+		break;
+	case HID_FEATURE_REPORT:
+		switch (reqtype) {
+		case HID_REQ_GET_REPORT:
+			// The EC doesn't respond to GET FEATURE for these touchpad reports
+			// we immediately discard to avoid waiting for a timeout.
+			if (reportnum == 6 || reportnum == 7 || reportnum == 8 || reportnum == 9 || reportnum == 0x0b) {
+				hid_dbg(hid, "%s: skipping get feature report for 0x%02x\n", __func__, reportnum);
+				return 0;
+			}
+
+			cid = 0x02;
+			break;
+		case HID_REQ_SET_REPORT:
+			cid = 0x03;
+			break;
+		default:
+			hid_err(hid, "%s: unknown req type 0x%02x\n", __func__, rtype);
+			return -EIO;
+		}
+		break;
+	default:
+		hid_err(hid, "%s: unknown report type 0x%02x\n", __func__, reportnum);
+		return -EIO;
+	}
+
+	rqst.target_category = SSAM_SSH_TC_HID;
+	rqst.channel = 0x02;
+	rqst.instance_id = vhf->p->instance;
+	rqst.command_id = cid;
+	rqst.flags = reqtype == HID_REQ_GET_REPORT ? SSAM_REQUEST_HAS_RESPONSE : 0;
+	rqst.length = reqtype == HID_REQ_GET_REPORT ? 1 : len;
+	rqst.payload = buf;
+
+	rsp.capacity = len;
+	rsp.length = 0;
+	rsp.pointer = buf;
+
+	hid_dbg(hid, "%s: sending to cid=%#04x snc=%#04x\n", __func__, cid, HID_REQ_GET_REPORT == reqtype);
+
+	status = ssam_request_sync(vhf->ctrl, &rqst, &rsp);
+	hid_dbg(hid, "%s: status %i\n", __func__, status);
+
+	if (status)
+		return status;
+
+	if (rsp.length > 0)
+		print_hex_dump_debug("response:", DUMP_PREFIX_OFFSET, 16, 1, rsp.pointer, rsp.length, false);
+
+	return rsp.length;
+}
+
+static struct hid_ll_driver sid_vhf_hid_ll_driver = {
+	.start         = sid_vhf_hid_start,
+	.stop          = sid_vhf_hid_stop,
+	.open          = sid_vhf_hid_open,
+	.close         = sid_vhf_hid_close,
+	.parse         = sid_vhf_hid_parse,
+	.raw_request   = sid_vhf_hid_raw_request,
+};
+
+
+static struct hid_device *sid_vhf_create_hid_device(struct platform_device *pdev, struct vhf_device_metadata *meta)
+{
+	struct hid_device *hid;
+
+	hid = hid_allocate_device();
+	if (IS_ERR(hid))
+		return hid;
+
+	hid->dev.parent = &pdev->dev;
+
+	hid->bus     = BUS_VIRTUAL;
+	hid->vendor  = meta->vendor_id;
+	hid->product = meta->product_id;
+
+	hid->ll_driver = &sid_vhf_hid_ll_driver;
+
+	sprintf(hid->name, "%s", SID_VHF_INPUT_NAME);
+
+	return hid;
+}
+
+static u32 sid_vhf_event_handler(struct ssam_notifier_block *nb, const struct ssam_event *event)
+{
+	struct sid_vhf *vhf = container_of(nb, struct sid_vhf, notif.base);
+	int status;
+
+	if (event->target_category != SSAM_SSH_TC_HID)
+		return 0;
+
+	if (event->channel != 0x02)
+		return 0;
+
+	if (event->instance_id != vhf->p->instance)
+		return 0;
+
+	if (event->command_id != 0x00 && event->command_id != 0x03 && event->command_id != 0x04)
+		return 0;
+
+	// skip if HID hasn't started yet
+	if (!test_bit(VHF_HID_STARTED, &vhf->state))
+		return SSAM_NOTIF_HANDLED;
+
+	status = hid_input_report(vhf->hid, HID_INPUT_REPORT, (u8 *)&event->data[0], event->length, 0);
+	return ssam_notifier_from_errno(status) | SSAM_NOTIF_HANDLED;
+}
+
+static int surface_sam_sid_vhf_probe(struct platform_device *pdev)
+{
+	const struct ssam_hid_properties *p = pdev->dev.platform_data;
+	struct ssam_controller *ctrl;
+	struct sid_vhf *vhf;
+	struct vhf_device_metadata meta = {};
+	struct hid_device *hid;
+	int status;
+
+	// add device link to EC
+	status = ssam_client_bind(&pdev->dev, &ctrl);
+	if (status)
+		return status == -ENXIO ? -EPROBE_DEFER : status;
+
+	vhf = kzalloc(sizeof(struct sid_vhf), GFP_KERNEL);
+	if (!vhf)
+		return -ENOMEM;
+
+	status = vhf_get_metadata(ctrl, p->instance, &meta);
+	if (status)
+		goto err_create_hid;
+
+	hid = sid_vhf_create_hid_device(pdev, &meta);
+	if (IS_ERR(hid)) {
+		status = PTR_ERR(hid);
+		goto err_create_hid;
+	}
+
+	vhf->dev = pdev;
+	vhf->ctrl = ctrl;
+	vhf->p = pdev->dev.platform_data;
+	vhf->hid = hid;
+
+	vhf->notif.base.priority = 1;
+	vhf->notif.base.fn = sid_vhf_event_handler;
+	vhf->notif.event.reg = p->registry;
+	vhf->notif.event.id.target_category = SSAM_SSH_TC_HID;
+	vhf->notif.event.id.instance = p->instance;
+	vhf->notif.event.flags = 0;
+
+	platform_set_drvdata(pdev, vhf);
+
+	status = ssam_notifier_register(ctrl, &vhf->notif);
+	if (status)
+		goto err_notif;
+
+	status = hid_add_device(hid);
+	if (status)
+		goto err_add_hid;
+
+	return 0;
+
+err_add_hid:
+	ssam_notifier_unregister(ctrl, &vhf->notif);
+err_notif:
+	hid_destroy_device(hid);
+	platform_set_drvdata(pdev, NULL);
+err_create_hid:
+	kfree(vhf);
+	return status;
+}
+
+static int surface_sam_sid_vhf_remove(struct platform_device *pdev)
+{
+	struct sid_vhf *vhf = platform_get_drvdata(pdev);
+
+	ssam_notifier_unregister(vhf->ctrl, &vhf->notif);
+	hid_destroy_device(vhf->hid);
+	kfree(vhf);
+
+	platform_set_drvdata(pdev, NULL);
+	return 0;
+}
+
+static struct platform_driver surface_sam_sid_vhf = {
+	.probe = surface_sam_sid_vhf_probe,
+	.remove = surface_sam_sid_vhf_remove,
+	.driver = {
+		.name = "surface_sam_sid_vhf",
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+module_platform_driver(surface_sam_sid_vhf);
+
+MODULE_AUTHOR("Blaž Hrastnik <blaz@mxxn.io>");
+MODULE_DESCRIPTION("Driver for HID devices connected via Surface SAM");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:surface_sam_sid_vhf");
diff --git a/drivers/platform/x86/surface_sam/surface_sam_sid_vhf.h b/drivers/platform/x86/surface_sam/surface_sam_sid_vhf.h
new file mode 100644
index 000000000000..d956de5cf877
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_sid_vhf.h
@@ -0,0 +1,14 @@
+
+#ifndef _SURFACE_SAM_SID_VHF_H
+#define _SURFACE_SAM_SID_VHF_H
+
+#include <linux/types.h>
+#include "surface_sam_ssh.h"
+
+
+struct ssam_hid_properties {
+	struct ssam_event_registry registry;
+	u8 instance;
+};
+
+#endif /* _SURFACE_SAM_SID_VHF_H */
diff --git a/drivers/platform/x86/surface_sam/surface_sam_ssh.c b/drivers/platform/x86/surface_sam/surface_sam_ssh.c
new file mode 100644
index 000000000000..4551b75570f2
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_ssh.c
@@ -0,0 +1,5329 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Surface Serial Hub (SSH) driver for communication with the Surface/System
+ * Aggregator Module.
+ */
+
+#include <asm/unaligned.h>
+#include <linux/acpi.h>
+#include <linux/atomic.h>
+#include <linux/completion.h>
+#include <linux/crc-ccitt.h>
+#include <linux/dmaengine.h>
+#include <linux/gpio/consumer.h>
+#include <linux/interrupt.h>
+#include <linux/jiffies.h>
+#include <linux/kernel.h>
+#include <linux/kfifo.h>
+#include <linux/kref.h>
+#include <linux/kthread.h>
+#include <linux/ktime.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/pm.h>
+#include <linux/refcount.h>
+#include <linux/serdev.h>
+#include <linux/spinlock.h>
+#include <linux/sysfs.h>
+#include <linux/workqueue.h>
+
+#include "surface_sam_ssh.h"
+
+#define CREATE_TRACE_POINTS
+#include "surface_sam_ssh_trace.h"
+
+
+/* -- Error injection helpers. ---------------------------------------------- */
+
+#ifdef CONFIG_SURFACE_SAM_SSH_ERROR_INJECTION
+#define noinline_if_inject noinline
+#else /* CONFIG_SURFACE_SAM_SSH_ERROR_INJECTION */
+#define noinline_if_inject inline
+#endif /* CONFIG_SURFACE_SAM_SSH_ERROR_INJECTION */
+
+
+/* -- SSH protocol utility functions and definitions. ----------------------- */
+
+/*
+ * The number of reserved event IDs, used for registering an SSH event
+ * handler. Valid event IDs are numbers below or equal to this value, with
+ * exception of zero, which is not an event ID. Thus, this is also the
+ * absolute maximum number of event handlers that can be registered.
+ */
+#define SSH_NUM_EVENTS		34
+
+/*
+ * The number of communication channels used in the protocol.
+ */
+#define SSH_NUM_CHANNELS	2
+
+
+static inline u16 ssh_crc(const u8 *buf, size_t len)
+{
+	return crc_ccitt_false(0xffff, buf, len);
+}
+
+static inline u16 ssh_rqid_next_valid(u16 rqid)
+{
+	return rqid > 0 ? rqid + 1u : rqid + SSH_NUM_EVENTS + 1u;
+}
+
+static inline u16 ssh_rqid_to_event(u16 rqid)
+{
+	return rqid - 1u;
+}
+
+static inline bool ssh_rqid_is_event(u16 rqid)
+{
+	return ssh_rqid_to_event(rqid) < SSH_NUM_EVENTS;
+}
+
+static inline int ssh_tc_to_rqid(u8 tc)
+{
+	return tc;
+}
+
+static inline u8 ssh_channel_to_index(u8 channel)
+{
+	return channel - 1u;
+}
+
+static inline bool ssh_channel_is_valid(u8 channel)
+{
+	return ssh_channel_to_index(channel) < SSH_NUM_CHANNELS;
+}
+
+
+/* -- Safe counters. -------------------------------------------------------- */
+
+struct ssh_seq_counter {
+	u8 value;
+};
+
+struct ssh_rqid_counter {
+	u16 value;
+};
+
+static inline void ssh_seq_reset(struct ssh_seq_counter *c)
+{
+	WRITE_ONCE(c->value, 0);
+}
+
+static inline u8 ssh_seq_next(struct ssh_seq_counter *c)
+{
+	u8 old = READ_ONCE(c->value);
+	u8 new = old + 1;
+	u8 ret;
+
+	while (unlikely((ret = cmpxchg(&c->value, old, new)) != old)) {
+		old = ret;
+		new = old + 1;
+	}
+
+	return old;
+}
+
+static inline void ssh_rqid_reset(struct ssh_rqid_counter *c)
+{
+	WRITE_ONCE(c->value, 0);
+}
+
+static inline u16 ssh_rqid_next(struct ssh_rqid_counter *c)
+{
+	u16 old = READ_ONCE(c->value);
+	u16 new = ssh_rqid_next_valid(old);
+	u16 ret;
+
+	while (unlikely((ret = cmpxchg(&c->value, old, new)) != old)) {
+		old = ret;
+		new = ssh_rqid_next_valid(old);
+	}
+
+	return old;
+}
+
+
+/* -- Builder functions for SAM-over-SSH messages. -------------------------- */
+
+struct msgbuf {
+	u8 *begin;
+	u8 *end;
+	u8 *ptr;
+};
+
+static inline void msgb_init(struct msgbuf *msgb, u8 *ptr, size_t cap)
+{
+	msgb->begin = ptr;
+	msgb->end = ptr + cap;
+	msgb->ptr = ptr;
+}
+
+static inline size_t msgb_bytes_used(const struct msgbuf *msgb)
+{
+	return msgb->ptr - msgb->begin;
+}
+
+static inline void msgb_push_u16(struct msgbuf *msgb, u16 value)
+{
+	if (WARN_ON(msgb->ptr + sizeof(u16) > msgb->end))
+		return;
+
+	put_unaligned_le16(value, msgb->ptr);
+	msgb->ptr += sizeof(u16);
+}
+
+static inline void msgb_push_syn(struct msgbuf *msgb)
+{
+	msgb_push_u16(msgb, SSH_MSG_SYN);
+}
+
+static inline void msgb_push_buf(struct msgbuf *msgb, const u8 *buf, size_t len)
+{
+	msgb->ptr = memcpy(msgb->ptr, buf, len) + len;
+}
+
+static inline void msgb_push_crc(struct msgbuf *msgb, const u8 *buf, size_t len)
+{
+	msgb_push_u16(msgb, ssh_crc(buf, len));
+}
+
+static inline void msgb_push_frame(struct msgbuf *msgb, u8 ty, u16 len, u8 seq)
+{
+	struct ssh_frame *frame = (struct ssh_frame *)msgb->ptr;
+	const u8 *const begin = msgb->ptr;
+
+	if (WARN_ON(msgb->ptr + sizeof(*frame) > msgb->end))
+		return;
+
+	frame->type = ty;
+	put_unaligned_le16(len, &frame->len);
+	frame->seq  = seq;
+
+	msgb->ptr += sizeof(*frame);
+	msgb_push_crc(msgb, begin, msgb->ptr - begin);
+}
+
+static inline void msgb_push_ack(struct msgbuf *msgb, u8 seq)
+{
+	// SYN
+	msgb_push_syn(msgb);
+
+	// ACK-type frame + CRC
+	msgb_push_frame(msgb, SSH_FRAME_TYPE_ACK, 0x00, seq);
+
+	// payload CRC (ACK-type frames do not have a payload)
+	msgb_push_crc(msgb, msgb->ptr, 0);
+}
+
+static inline void msgb_push_nak(struct msgbuf *msgb)
+{
+	// SYN
+	msgb_push_syn(msgb);
+
+	// NAK-type frame + CRC
+	msgb_push_frame(msgb, SSH_FRAME_TYPE_NAK, 0x00, 0x00);
+
+	// payload CRC (ACK-type frames do not have a payload)
+	msgb_push_crc(msgb, msgb->ptr, 0);
+}
+
+static inline void msgb_push_cmd(struct msgbuf *msgb, u8 seq, u16 rqid,
+				 const struct ssam_request *rqst)
+{
+	struct ssh_command *cmd;
+	const u8 *cmd_begin;
+	const u8 type = SSH_FRAME_TYPE_DATA_SEQ;
+
+	// SYN
+	msgb_push_syn(msgb);
+
+	// command frame + crc
+	msgb_push_frame(msgb, type, sizeof(*cmd) + rqst->length, seq);
+
+	// frame payload: command struct + payload
+	if (WARN_ON(msgb->ptr + sizeof(*cmd) > msgb->end))
+		return;
+
+	cmd_begin = msgb->ptr;
+	cmd = (struct ssh_command *)msgb->ptr;
+
+	cmd->type    = SSH_PLD_TYPE_CMD;
+	cmd->tc      = rqst->target_category;
+	cmd->chn_out = rqst->channel;
+	cmd->chn_in  = 0x00;
+	cmd->iid     = rqst->instance_id;
+	put_unaligned_le16(rqid, &cmd->rqid);
+	cmd->cid     = rqst->command_id;
+
+	msgb->ptr += sizeof(*cmd);
+
+	// command payload
+	msgb_push_buf(msgb, rqst->payload, rqst->length);
+
+	// crc for command struct + payload
+	msgb_push_crc(msgb, cmd_begin, msgb->ptr - cmd_begin);
+}
+
+
+/* -- Parser functions and utilities for SAM-over-SSH messages. ------------- */
+
+struct sshp_buf {
+	u8    *ptr;
+	size_t len;
+	size_t cap;
+};
+
+
+static inline bool sshp_validate_crc(const struct ssam_span *src, const u8 *crc)
+{
+	u16 actual = ssh_crc(src->ptr, src->len);
+	u16 expected = get_unaligned_le16(crc);
+
+	return actual == expected;
+}
+
+static bool sshp_find_syn(const struct ssam_span *src, struct ssam_span *rem)
+{
+	size_t i;
+
+	for (i = 0; i < src->len - 1; i++) {
+		if (likely(get_unaligned_le16(src->ptr + i) == SSH_MSG_SYN)) {
+			rem->ptr = src->ptr + i;
+			rem->len = src->len - i;
+			return true;
+		}
+	}
+
+	if (unlikely(src->ptr[src->len - 1] == (SSH_MSG_SYN & 0xff))) {
+		rem->ptr = src->ptr + src->len - 1;
+		rem->len = 1;
+		return false;
+	} else {
+		rem->ptr = src->ptr + src->len;
+		rem->len = 0;
+		return false;
+	}
+}
+
+static bool sshp_starts_with_syn(const struct ssam_span *src)
+{
+	return src->len >= 2 && get_unaligned_le16(src->ptr) == SSH_MSG_SYN;
+}
+
+static int sshp_parse_frame(const struct device *dev,
+			    const struct ssam_span *source,
+			    struct ssh_frame **frame,
+			    struct ssam_span *payload,
+			    size_t maxlen)
+{
+	struct ssam_span sf;
+	struct ssam_span sp;
+
+	// initialize output
+	*frame = NULL;
+	payload->ptr = NULL;
+	payload->len = 0;
+
+	if (!sshp_starts_with_syn(source)) {
+		dev_warn(dev, "rx: parser: invalid start of frame\n");
+		return -ENOMSG;
+	}
+
+	// check for minumum packet length
+	if (unlikely(source->len < SSH_MESSAGE_LENGTH(0))) {
+		dev_dbg(dev, "rx: parser: not enough data for frame\n");
+		return 0;
+	}
+
+	// pin down frame
+	sf.ptr = source->ptr + sizeof(u16);
+	sf.len = sizeof(struct ssh_frame);
+
+	// validate frame CRC
+	if (unlikely(!sshp_validate_crc(&sf, sf.ptr + sf.len))) {
+		dev_warn(dev, "rx: parser: invalid frame CRC\n");
+		return -EBADMSG;
+	}
+
+	// ensure packet does not exceed maximum length
+	if (unlikely(((struct ssh_frame *)sf.ptr)->len > maxlen)) {
+		dev_warn(dev, "rx: parser: frame too large: %u bytes\n",
+			 ((struct ssh_frame *)sf.ptr)->len);
+		return -EMSGSIZE;
+	}
+
+	// pin down payload
+	sp.ptr = sf.ptr + sf.len + sizeof(u16);
+	sp.len = get_unaligned_le16(&((struct ssh_frame *)sf.ptr)->len);
+
+	// check for frame + payload length
+	if (source->len < SSH_MESSAGE_LENGTH(sp.len)) {
+		dev_dbg(dev, "rx: parser: not enough data for payload\n");
+		return 0;
+	}
+
+	// validate payload crc
+	if (unlikely(!sshp_validate_crc(&sp, sp.ptr + sp.len))) {
+		dev_warn(dev, "rx: parser: invalid payload CRC\n");
+		return -EBADMSG;
+	}
+
+	*frame = (struct ssh_frame *)sf.ptr;
+	*payload = sp;
+
+	dev_dbg(dev, "rx: parser: valid frame found (type: 0x%02x, len: %u)\n",
+		(*frame)->type, (*frame)->len);
+
+	return 0;
+}
+
+static int sshp_parse_command(const struct device *dev,
+			      const struct ssam_span *source,
+			      struct ssh_command **command,
+			      struct ssam_span *command_data)
+{
+	// check for minimum length
+	if (unlikely(source->len < sizeof(struct ssh_command))) {
+		*command = NULL;
+		command_data->ptr = NULL;
+		command_data->len = 0;
+
+		dev_err(dev, "rx: parser: command payload is too short\n");
+		return -ENOMSG;
+	}
+
+	*command = (struct ssh_command *)source->ptr;
+	command_data->ptr = source->ptr + sizeof(struct ssh_command);
+	command_data->len = source->len - sizeof(struct ssh_command);
+
+	dev_dbg(dev, "rx: parser: valid command found (tc: 0x%02x,"
+		" cid: 0x%02x)\n", (*command)->tc, (*command)->cid);
+
+	return 0;
+}
+
+
+static inline void sshp_buf_init(struct sshp_buf *buf, u8 *ptr, size_t cap)
+{
+	buf->ptr = ptr;
+	buf->len = 0;
+	buf->cap = cap;
+}
+
+static inline int sshp_buf_alloc(struct sshp_buf *buf, size_t cap, gfp_t flags)
+{
+	u8 *ptr;
+
+	ptr = kzalloc(cap, flags);
+	if (!ptr)
+		return -ENOMEM;
+
+	sshp_buf_init(buf, ptr, cap);
+	return 0;
+
+}
+
+static inline void sshp_buf_free(struct sshp_buf *buf)
+{
+	kfree(buf->ptr);
+	buf->ptr = NULL;
+	buf->len = 0;
+	buf->cap = 0;
+}
+
+static inline void sshp_buf_drop(struct sshp_buf *buf, size_t n)
+{
+	memmove(buf->ptr, buf->ptr + n, buf->len - n);
+	buf->len -= n;
+}
+
+static inline size_t sshp_buf_read_from_fifo(struct sshp_buf *buf,
+					     struct kfifo *fifo)
+{
+	size_t n;
+
+	n =  kfifo_out(fifo, buf->ptr + buf->len, buf->cap - buf->len);
+	buf->len += n;
+
+	return n;
+}
+
+static inline void sshp_buf_span_from(struct sshp_buf *buf, size_t offset,
+				      struct ssam_span *span)
+{
+	span->ptr = buf->ptr + offset;
+	span->len = buf->len - offset;
+}
+
+
+/* -- Packet transport layer (ptl). ----------------------------------------- */
+/*
+ * To simplify reasoning about the code below, we define a few concepts. The
+ * system below is similar to a state-machine for packets, however, there are
+ * too many states to explicitly write them down. To (somewhat) manage the
+ * states and packets we rely on flags, reference counting, and some simple
+ * concepts. State transitions are triggered by actions.
+ *
+ * >> Actions <<
+ *
+ * - submit
+ * - transmission start (process next item in queue)
+ * - transmission finished (guaranteed to never be parallel to transmission
+ *   start)
+ * - ACK received
+ * - NAK received (this is equivalent to issuing re-submit for all pending
+ *   packets)
+ * - timeout (this is equivalent to re-issuing a submit or canceling)
+ * - cancel (non-pending and pending)
+ *
+ * >> Data Structures, Packet Ownership, General Overview <<
+ *
+ * The code below employs two main data structures: The packet queue, containing
+ * all packets scheduled for transmission, and the set of pending packets,
+ * containing all packets awaiting an ACK.
+ *
+ * Shared ownership of a packet is controlled via reference counting. Inside the
+ * transmission system are a total of five packet owners:
+ *
+ * - the packet queue,
+ * - the pending set,
+ * - the transmitter thread,
+ * - the receiver thread (via ACKing), and
+ * - the timeout work item.
+ *
+ * Normal operation is as follows: The initial reference of the packet is
+ * obtained by submitting the packet and queueing it. The receiver thread
+ * takes packets from the queue. By doing this, it does not increment the
+ * refcount but takes over the reference (removing it from the queue).
+ * If the packet is sequenced (i.e. needs to be ACKed by the client), the
+ * transmitter thread sets-up the timeout and adds the packet to the pending set
+ * before starting to transmit it. As the timeout is handled by a reaper task,
+ * no additional reference for it is needed. After the transmit is done, the
+ * reference hold by the transmitter thread is dropped. If the packet is
+ * unsequenced (i.e. does not need an ACK), the packet is completed by the
+ * transmitter thread before dropping that reference.
+ *
+ * On receial of an ACK, the receiver thread removes and obtains the refernce to
+ * the packet from the pending set. On succes, the receiver thread will then
+ * complete the packet and drop its reference.
+ *
+ * On error, the completion callback is immediately run by on thread on which
+ * the error was detected.
+ *
+ * To ensure that a packet eventually leaves the system it is marked as "locked"
+ * directly before it is going to be completed or when it is canceled. Marking a
+ * packet as "locked" has the effect that passing and creating new references
+ * of the packet will be blocked. This means that the packet cannot be added
+ * to the queue, the pending set, and the timeout, or be picked up by the
+ * transmitter thread or receiver thread. To remove a packet from the system it
+ * has to be marked as locked and subsequently all references from the data
+ * structures (queue, pending) have to be removed. References held by threads
+ * will eventually be dropped automatically as their execution progresses.
+ *
+ * Note that the packet completion callback is, in case of success and for a
+ * sequenced packet, guaranteed to run on the receiver thread, thus providing a
+ * way to reliably identify responses to the packet. The packet completion
+ * callback is only run once and it does not indicate that the packet has fully
+ * left the system. In case of re-submission (and with somewhat unlikely
+ * timing), it may be possible that the packet is being re-transmitted while the
+ * completion callback runs. Completion will occur both on success and internal
+ * error, as well as when the packet is canceled.
+ *
+ * >> Flags <<
+ *
+ * Flags are used to indicate the state and progression of a packet. Some flags
+ * have stricter guarantees than other:
+ *
+ * - locked
+ *   Indicates if the packet is locked. If the packet is locked, passing and/or
+ *   creating additional references to the packet is forbidden. The packet thus
+ *   may not be queued, dequeued, or removed or added to the pending set. Note
+ *   that the packet state flags may still change (e.g. it may be marked as
+ *   ACKed, transmitted, ...).
+ *
+ * - completed
+ *   Indicates if the packet completion has been run or is about to be run. This
+ *   flag is used to ensure that the packet completion callback is only run
+ *   once.
+ *
+ * - queued
+ *   Indicates if a packet is present in the submission queue or not. This flag
+ *   must only be modified with the queue lock held, and must be coherent
+ *   presence of the packet in the queue.
+ *
+ * - pending
+ *   Indicates if a packet is present in the set of pending packets or not.
+ *   This flag must only be modified with the pending lock held, and must be
+ *   coherent presence of the packet in the pending set.
+ *
+ * - transmitting
+ *   Indicates if the packet is currently transmitting. In case of
+ *   re-transmissions, it is only safe to wait on the "transmitted" completion
+ *   after this flag has been set. The completion will be set both in success
+ *   and error case.
+ *
+ * - transmitted
+ *   Indicates if the packet has been transmitted. This flag is not cleared by
+ *   the system, thus it indicates the first transmission only.
+ *
+ * - acked
+ *   Indicates if the packet has been acknowledged by the client. There are no
+ *   other guarantees given. For example, the packet may still be canceled
+ *   and/or the completion may be triggered an error even though this bit is
+ *   set. Rely on the status provided by completion instead.
+ *
+ * - canceled
+ *   Indicates if the packet has been canceled from the outside. There are no
+ *   other guarantees given. Specifically, the packet may be completed by
+ *   another part of the system before the cancellation attempts to complete it.
+ *
+ * >> General Notes <<
+ *
+ * To avoid deadlocks, if both queue and pending locks are required, the pending
+ * lock must be acquired before the queue lock.
+ */
+
+/**
+ * Maximum number transmission attempts per sequenced packet in case of
+ * time-outs. Must be smaller than 16.
+ */
+#define SSH_PTL_MAX_PACKET_TRIES	3
+
+/**
+ * Timeout as ktime_t delta for ACKs. If we have not received an ACK in this
+ * time-frame after starting transmission, the packet will be re-submitted.
+ */
+#define SSH_PTL_PACKET_TIMEOUT			ms_to_ktime(1000)
+
+/**
+ * Maximum time resolution for timeouts. Currently set to max(2 jiffies, 50ms).
+ * Should be larger than one jiffy to avoid direct re-scheduling of reaper
+ * work_struct.
+ */
+#define SSH_PTL_PACKET_TIMEOUT_RESOLUTION	ms_to_ktime(max(2000 / HZ, 50))
+
+/**
+ * Maximum number of sequenced packets concurrently waiting for an ACK.
+ * Packets marked as blocking will not be transmitted while this limit is
+ * reached.
+ */
+#define SSH_PTL_MAX_PENDING		1
+
+#define SSH_PTL_RX_BUF_LEN		4096
+
+#define SSH_PTL_RX_FIFO_LEN		4096
+
+
+enum ssh_ptl_state_flags {
+	SSH_PTL_SF_SHUTDOWN_BIT,
+};
+
+struct ssh_ptl_ops {
+	void (*data_received)(struct ssh_ptl *p, const struct ssam_span *data);
+};
+
+struct ssh_ptl {
+	struct serdev_device *serdev;
+	unsigned long state;
+
+	struct {
+		spinlock_t lock;
+		struct list_head head;
+	} queue;
+
+	struct {
+		spinlock_t lock;
+		struct list_head head;
+		atomic_t count;
+	} pending;
+
+	struct {
+		bool thread_signal;
+		struct task_struct *thread;
+		struct wait_queue_head thread_wq;
+		struct wait_queue_head packet_wq;
+		struct ssh_packet *packet;
+		size_t offset;
+	} tx;
+
+	struct {
+		struct task_struct *thread;
+		struct wait_queue_head wq;
+		struct kfifo fifo;
+		struct sshp_buf buf;
+
+		struct {
+			u16 seqs[8];
+			u16 offset;
+		} blocked;
+	} rx;
+
+	struct {
+		ktime_t timeout;
+		ktime_t expires;
+		struct delayed_work reaper;
+	} rtx_timeout;
+
+	struct ssh_ptl_ops ops;
+};
+
+
+#define __ssam_prcond(func, p, fmt, ...)		\
+	do {						\
+		if ((p))				\
+			func((p), fmt, ##__VA_ARGS__);	\
+	} while (0);
+
+#define ptl_dbg(p, fmt, ...)  dev_dbg(&(p)->serdev->dev, fmt, ##__VA_ARGS__)
+#define ptl_info(p, fmt, ...) dev_info(&(p)->serdev->dev, fmt, ##__VA_ARGS__)
+#define ptl_warn(p, fmt, ...) dev_warn(&(p)->serdev->dev, fmt, ##__VA_ARGS__)
+#define ptl_err(p, fmt, ...)  dev_err(&(p)->serdev->dev, fmt, ##__VA_ARGS__)
+#define ptl_dbg_cond(p, fmt, ...) __ssam_prcond(ptl_dbg, p, fmt, ##__VA_ARGS__)
+
+#define to_ssh_packet(ptr, member) \
+	container_of(ptr, struct ssh_packet, member)
+
+#define to_ssh_ptl(ptr, member) \
+	container_of(ptr, struct ssh_ptl, member)
+
+
+#ifdef CONFIG_SURFACE_SAM_SSH_ERROR_INJECTION
+
+/**
+ * ssh_ptl_should_drop_ack_packet - error injection hook to drop ACK packets
+ *
+ * Useful to test detection and handling of automated re-transmits by the EC.
+ * Specifically of packets that the EC consideres not-ACKed but the driver
+ * already consideres ACKed (due to dropped ACK). In this case, the EC
+ * re-transmits the packet-to-be-ACKed and the driver should detect it as
+ * duplicate/already handled. Note that the driver should still send an ACK
+ * for the re-transmitted packet.
+ */
+static noinline bool ssh_ptl_should_drop_ack_packet(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_drop_ack_packet, TRUE);
+
+/**
+ * ssh_ptl_should_drop_nak_packet - error injection hook to drop NAK packets
+ *
+ * Useful to test/force automated (timeout-based) re-transmit by the EC.
+ * Specifically, packets that have not reached the driver completely/with valid
+ * checksums. Only useful in combination with receival of (injected) bad data.
+ */
+static noinline bool ssh_ptl_should_drop_nak_packet(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_drop_nak_packet, TRUE);
+
+/**
+ * ssh_ptl_should_drop_dsq_packet - error injection hook to drop sequenced data
+ * packet
+ *
+ * Useful to test re-transmit timeout of the driver. If the data packet has not
+ * been ACKed after a certain time, the driver should re-transmit the packet up
+ * to limited number of times defined in SSH_PTL_MAX_PACKET_TRIES.
+ */
+static noinline bool ssh_ptl_should_drop_dsq_packet(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_drop_dsq_packet, TRUE);
+
+/**
+ * ssh_ptl_should_fail_write - error injection hook to make serdev_device_write
+ * fail
+ *
+ * Hook to simulate errors in serdev_device_write when transmitting packets.
+ */
+static noinline int ssh_ptl_should_fail_write(void)
+{
+	return 0;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_fail_write, ERRNO);
+
+/**
+ * ssh_ptl_should_corrupt_tx_data - error injection hook to simualte invalid
+ * data being sent to the EC
+ *
+ * Hook to simulate corrupt/invalid data being sent from host (driver) to EC.
+ * Causes the packet data to be actively corrupted by overwriting it with
+ * pre-defined values, such that it becomes invalid, causing the EC to respond
+ * with a NAK packet. Useful to test handling of NAK packets received by the
+ * driver.
+ */
+static noinline bool ssh_ptl_should_corrupt_tx_data(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_corrupt_tx_data, TRUE);
+
+/**
+ * ssh_ptl_should_corrupt_rx_syn - error injection hook to simulate invalid
+ * data being sent by the EC
+ *
+ * Hook to simulate invalid SYN bytes, i.e. an invalid start of messages and
+ * test handling thereof in the driver.
+ */
+static noinline bool ssh_ptl_should_corrupt_rx_syn(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_corrupt_rx_syn, TRUE);
+
+/**
+ * ssh_ptl_should_corrupt_rx_data - error injection hook to simulate invalid
+ * data being sent by the EC
+ *
+ * Hook to simulate invalid data/checksum of the message frame and test handling
+ * thereof in the driver.
+ */
+static noinline bool ssh_ptl_should_corrupt_rx_data(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_corrupt_rx_data, TRUE);
+
+
+static inline bool __ssh_ptl_should_drop_ack_packet(struct ssh_packet *packet)
+{
+	if (likely(!ssh_ptl_should_drop_ack_packet()))
+		return false;
+
+	trace_ssam_ei_tx_drop_ack_packet(packet);
+	ptl_info(packet->ptl, "packet error injection: dropping ACK packet %p\n",
+		 packet);
+
+	return true;
+}
+
+static inline bool __ssh_ptl_should_drop_nak_packet(struct ssh_packet *packet)
+{
+	if (likely(!ssh_ptl_should_drop_nak_packet()))
+		return false;
+
+	trace_ssam_ei_tx_drop_nak_packet(packet);
+	ptl_info(packet->ptl, "packet error injection: dropping NAK packet %p\n",
+		 packet);
+
+	return true;
+}
+
+static inline bool __ssh_ptl_should_drop_dsq_packet(struct ssh_packet *packet)
+{
+	if (likely(!ssh_ptl_should_drop_dsq_packet()))
+		return false;
+
+	trace_ssam_ei_tx_drop_dsq_packet(packet);
+	ptl_info(packet->ptl,
+		"packet error injection: dropping sequenced data packet %p\n",
+		 packet);
+
+	return true;
+}
+
+static bool ssh_ptl_should_drop_packet(struct ssh_packet *packet)
+{
+	// ignore packets that don't carry any data (i.e. flush)
+	if (!packet->data.ptr || !packet->data.len)
+		return false;
+
+	switch (packet->data.ptr[SSH_MSGOFFSET_FRAME(type)]) {
+	case SSH_FRAME_TYPE_ACK:
+		return __ssh_ptl_should_drop_ack_packet(packet);
+
+	case SSH_FRAME_TYPE_NAK:
+		return __ssh_ptl_should_drop_nak_packet(packet);
+
+	case SSH_FRAME_TYPE_DATA_SEQ:
+		return __ssh_ptl_should_drop_dsq_packet(packet);
+
+	default:
+		return false;
+	}
+}
+
+static int ssh_ptl_write_buf(struct ssh_ptl *ptl, struct ssh_packet *packet,
+			     const unsigned char *buf, size_t count)
+{
+	int status;
+
+	status = ssh_ptl_should_fail_write();
+	if (unlikely(status)) {
+		trace_ssam_ei_tx_fail_write(packet, status);
+		ptl_info(packet->ptl,
+			 "packet error injection: simulating transmit error %d, packet %p\n",
+			 status, packet);
+
+		return status;
+	}
+
+	return serdev_device_write_buf(ptl->serdev, buf, count);
+}
+
+static void ssh_ptl_tx_inject_invalid_data(struct ssh_packet *packet)
+{
+	// ignore packets that don't carry any data (i.e. flush)
+	if (!packet->data.ptr || !packet->data.len)
+		return;
+
+	// only allow sequenced data packets to be modified
+	if (packet->data.ptr[SSH_MSGOFFSET_FRAME(type)] != SSH_FRAME_TYPE_DATA_SEQ)
+		return;
+
+	if (likely(!ssh_ptl_should_corrupt_tx_data()))
+		return;
+
+	trace_ssam_ei_tx_corrupt_data(packet);
+	ptl_info(packet->ptl,
+		 "packet error injection: simulating invalid transmit data on packet %p\n",
+		 packet);
+
+	/*
+	 * NB: The value 0xb3 has been chosen more or less randomly so that it
+	 * doesn't have any (major) overlap with the SYN bytes (aa 55) and is
+	 * non-trivial (i.e. non-zero, non-0xff).
+	 */
+	memset(packet->data.ptr, 0xb3, packet->data.len);
+}
+
+static void ssh_ptl_rx_inject_invalid_syn(struct ssh_ptl *ptl,
+					  struct ssam_span *data)
+{
+	struct ssam_span frame;
+
+	// check if there actually is something to corrupt
+	if (!sshp_find_syn(data, &frame))
+		return;
+
+	if (likely(!ssh_ptl_should_corrupt_rx_syn()))
+		return;
+
+	trace_ssam_ei_rx_corrupt_syn("data_length", data->len);
+
+	data->ptr[1] = 0xb3;	// set second byte of SYN to "random" value
+}
+
+static void ssh_ptl_rx_inject_invalid_data(struct ssh_ptl *ptl,
+					   struct ssam_span *frame)
+{
+	size_t payload_len, message_len;
+	struct ssh_frame *sshf;
+
+	// ignore incomplete messages, will get handled once it's complete
+	if (frame->len < SSH_MESSAGE_LENGTH(0))
+		return;
+
+	// ignore incomplete messages, part 2
+	payload_len = get_unaligned_le16(&frame->ptr[SSH_MSGOFFSET_FRAME(len)]);
+	message_len = SSH_MESSAGE_LENGTH(payload_len);
+	if (frame->len < message_len)
+		return;
+
+	if (likely(!ssh_ptl_should_corrupt_rx_data()))
+		return;
+
+	sshf = (struct ssh_frame *)&frame->ptr[SSH_MSGOFFSET_FRAME(type)];
+	trace_ssam_ei_rx_corrupt_data(sshf);
+
+	/*
+	 * Flip bits in first byte of payload checksum. This is basically
+	 * equivalent to a payload/frame data error without us having to worry
+	 * about (the, arguably pretty small, probability of) accidental
+	 * checksum collisions.
+	 */
+	frame->ptr[frame->len - 2] = ~frame->ptr[frame->len - 2];
+}
+
+#else /* CONFIG_SURFACE_SAM_SSH_ERROR_INJECTION */
+
+static inline bool ssh_ptl_should_drop_packet(struct ssh_packet *packet)
+{
+	return false;
+}
+
+static inline int ssh_ptl_write_buf(struct ssh_ptl *ptl,
+				    struct ssh_packet *packet,
+				    const unsigned char *buf,
+				    size_t count)
+{
+	return serdev_device_write_buf(ptl->serdev, buf, count);
+}
+
+static inline void ssh_ptl_tx_inject_invalid_data(struct ssh_packet *packet)
+{
+}
+
+static inline void ssh_ptl_rx_inject_invalid_syn(struct ssh_ptl *ptl,
+						 struct ssam_span *data)
+{
+}
+
+static inline void ssh_ptl_rx_inject_invalid_data(struct ssh_ptl *ptl,
+						  struct ssam_span *frame)
+{
+}
+
+#endif /* CONFIG_SURFACE_SAM_SSH_ERROR_INJECTION */
+
+
+static void __ssh_ptl_packet_release(struct kref *kref)
+{
+	struct ssh_packet *p = to_ssh_packet(kref, refcnt);
+
+	trace_ssam_packet_release(p);
+
+	ptl_dbg_cond(p->ptl, "ptl: releasing packet %p\n", p);
+	p->ops->release(p);
+}
+
+void ssh_packet_get(struct ssh_packet *packet)
+{
+	kref_get(&packet->refcnt);
+}
+EXPORT_SYMBOL_GPL(ssh_packet_get);
+
+void ssh_packet_put(struct ssh_packet *packet)
+{
+	kref_put(&packet->refcnt, __ssh_ptl_packet_release);
+}
+EXPORT_SYMBOL_GPL(ssh_packet_put);
+
+static inline u8 ssh_packet_get_seq(struct ssh_packet *packet)
+{
+	return packet->data.ptr[SSH_MSGOFFSET_FRAME(seq)];
+}
+
+
+struct ssh_packet_args {
+	unsigned long type;
+	u8 priority;
+	const struct ssh_packet_ops *ops;
+};
+
+static void ssh_packet_init(struct ssh_packet *packet,
+			    const struct ssh_packet_args *args)
+{
+	kref_init(&packet->refcnt);
+
+	packet->ptl = NULL;
+	INIT_LIST_HEAD(&packet->queue_node);
+	INIT_LIST_HEAD(&packet->pending_node);
+
+	packet->state = args->type & SSH_PACKET_FLAGS_TY_MASK;
+	packet->priority = args->priority;
+	packet->timestamp = KTIME_MAX;
+
+	packet->data.ptr = NULL;
+	packet->data.len = 0;
+
+	packet->ops = args->ops;
+}
+
+
+static struct kmem_cache *ssh_ctrl_packet_cache;
+
+static int __init ssh_ctrl_packet_cache_init(void)
+{
+	const unsigned int size = sizeof(struct ssh_packet) + SSH_MSG_LEN_CTRL;
+	const unsigned int align = __alignof__(struct ssh_packet);
+	struct kmem_cache *cache;
+
+	cache = kmem_cache_create("ssam_ctrl_packet", size, align, 0, NULL);
+	if (!cache)
+		return -ENOMEM;
+
+	ssh_ctrl_packet_cache = cache;
+	return 0;
+}
+
+static void __exit ssh_ctrl_packet_cache_destroy(void)
+{
+	kmem_cache_destroy(ssh_ctrl_packet_cache);
+	ssh_ctrl_packet_cache = NULL;
+}
+
+static int ssh_ctrl_packet_alloc(struct ssh_packet **packet,
+				 struct ssam_span *buffer, gfp_t flags)
+{
+	*packet = kmem_cache_alloc(ssh_ctrl_packet_cache, flags);
+	if (!*packet)
+		return -ENOMEM;
+
+	buffer->ptr = (u8 *)(*packet + 1);
+	buffer->len = SSH_MSG_LEN_CTRL;
+
+	trace_ssam_ctrl_packet_alloc(*packet, buffer->len);
+	return 0;
+}
+
+static void ssh_ctrl_packet_free(struct ssh_packet *p)
+{
+	trace_ssam_ctrl_packet_free(p);
+	kmem_cache_free(ssh_ctrl_packet_cache, p);
+}
+
+static const struct ssh_packet_ops ssh_ptl_ctrl_packet_ops = {
+	.complete = NULL,
+	.release = ssh_ctrl_packet_free,
+};
+
+
+static void ssh_ptl_timeout_reaper_mod(struct ssh_ptl *ptl, ktime_t now,
+				       ktime_t expires)
+{
+	unsigned long delta = msecs_to_jiffies(ktime_ms_delta(expires, now));
+	ktime_t aexp = ktime_add(expires, SSH_PTL_PACKET_TIMEOUT_RESOLUTION);
+	ktime_t old;
+
+	// re-adjust / schedule reaper if it is above resolution delta
+	old = READ_ONCE(ptl->rtx_timeout.expires);
+	while (ktime_before(aexp, old))
+		old = cmpxchg64(&ptl->rtx_timeout.expires, old, expires);
+
+	// if we updated the reaper expiration, modify work timeout
+	if (old == expires)
+		mod_delayed_work(system_wq, &ptl->rtx_timeout.reaper, delta);
+}
+
+static void ssh_ptl_timeout_start(struct ssh_packet *packet)
+{
+	struct ssh_ptl *ptl = packet->ptl;
+	ktime_t timestamp = ktime_get_coarse_boottime();
+	ktime_t timeout = ptl->rtx_timeout.timeout;
+
+	if (test_bit(SSH_PACKET_SF_LOCKED_BIT, &packet->state))
+		return;
+
+	WRITE_ONCE(packet->timestamp, timestamp);
+	smp_mb__after_atomic();
+
+	ssh_ptl_timeout_reaper_mod(packet->ptl, timestamp, timestamp + timeout);
+}
+
+
+static struct list_head *__ssh_ptl_queue_find_entrypoint(struct ssh_packet *p)
+{
+	struct list_head *head;
+	u8 priority = READ_ONCE(p->priority);
+
+	/*
+	 * We generally assume that there are less control (ACK/NAK) packets and
+	 * re-submitted data packets as there are normal data packets (at least
+	 * in situations in which many packets are queued; if there aren't many
+	 * packets queued the decision on how to iterate should be basically
+	 * irrellevant; the number of control/data packets is more or less
+	 * limited via the maximum number of pending packets). Thus, when
+	 * inserting a control or re-submitted data packet, (determined by their
+	 * priority), we search from front to back. Normal data packets are,
+	 * usually queued directly at the tail of the queue, so for those search
+	 * from back to front.
+	 */
+
+	if (priority > SSH_PACKET_PRIORITY_DATA) {
+		list_for_each(head, &p->ptl->queue.head) {
+			p = list_entry(head, struct ssh_packet, queue_node);
+
+			if (READ_ONCE(p->priority) < priority)
+				break;
+		}
+	} else {
+		list_for_each_prev(head, &p->ptl->queue.head) {
+			p = list_entry(head, struct ssh_packet, queue_node);
+
+			if (READ_ONCE(p->priority) >= priority) {
+				head = head->next;
+				break;
+			}
+		}
+	}
+
+
+	return head;
+}
+
+static int ssh_ptl_queue_push(struct ssh_packet *packet)
+{
+	struct ssh_ptl *ptl = packet->ptl;
+	struct list_head *head;
+
+	spin_lock(&ptl->queue.lock);
+
+	if (test_bit(SSH_PTL_SF_SHUTDOWN_BIT, &ptl->state)) {
+		spin_unlock(&ptl->queue.lock);
+		return -ESHUTDOWN;
+	}
+
+	// avoid further transitions when cancelling/completing
+	if (test_bit(SSH_PACKET_SF_LOCKED_BIT, &packet->state)) {
+		spin_unlock(&ptl->queue.lock);
+		return -EINVAL;
+	}
+
+	// if this packet has already been queued, do not add it
+	if (test_and_set_bit(SSH_PACKET_SF_QUEUED_BIT, &packet->state)) {
+		spin_unlock(&ptl->queue.lock);
+		return -EALREADY;
+	}
+
+	head = __ssh_ptl_queue_find_entrypoint(packet);
+
+	ssh_packet_get(packet);
+	list_add_tail(&packet->queue_node, &ptl->queue.head);
+
+	spin_unlock(&ptl->queue.lock);
+	return 0;
+}
+
+static void ssh_ptl_queue_remove(struct ssh_packet *packet)
+{
+	struct ssh_ptl *ptl = packet->ptl;
+	bool remove;
+
+	spin_lock(&ptl->queue.lock);
+
+	remove = test_and_clear_bit(SSH_PACKET_SF_QUEUED_BIT, &packet->state);
+	if (remove)
+		list_del(&packet->queue_node);
+
+	spin_unlock(&ptl->queue.lock);
+
+	if (remove)
+		ssh_packet_put(packet);
+}
+
+
+static void ssh_ptl_pending_push(struct ssh_packet *packet)
+{
+	struct ssh_ptl *ptl = packet->ptl;
+
+	spin_lock(&ptl->pending.lock);
+
+	// if we are cancelling/completing this packet, do not add it
+	if (test_bit(SSH_PACKET_SF_LOCKED_BIT, &packet->state)) {
+		spin_unlock(&ptl->pending.lock);
+		return;
+	}
+
+	// in case it is already pending (e.g. re-submission), do not add it
+	if (test_and_set_bit(SSH_PACKET_SF_PENDING_BIT, &packet->state)) {
+		spin_unlock(&ptl->pending.lock);
+		return;
+	}
+
+	atomic_inc(&ptl->pending.count);
+	ssh_packet_get(packet);
+	list_add_tail(&packet->pending_node, &ptl->pending.head);
+
+	spin_unlock(&ptl->pending.lock);
+}
+
+static void ssh_ptl_pending_remove(struct ssh_packet *packet)
+{
+	struct ssh_ptl *ptl = packet->ptl;
+	bool remove;
+
+	spin_lock(&ptl->pending.lock);
+
+	remove = test_and_clear_bit(SSH_PACKET_SF_PENDING_BIT, &packet->state);
+	if (remove) {
+		list_del(&packet->pending_node);
+		atomic_dec(&ptl->pending.count);
+	}
+
+	spin_unlock(&ptl->pending.lock);
+
+	if (remove)
+		ssh_packet_put(packet);
+}
+
+
+static void __ssh_ptl_complete(struct ssh_packet *p, int status)
+{
+	struct ssh_ptl *ptl = READ_ONCE(p->ptl);
+
+	trace_ssam_packet_complete(p, status);
+
+	ptl_dbg_cond(ptl, "ptl: completing packet %p\n", p);
+	if (status && status != -ECANCELED)
+		ptl_dbg_cond(ptl, "ptl: packet error: %d\n", status);
+
+	if (p->ops->complete)
+		p->ops->complete(p, status);
+}
+
+static void ssh_ptl_remove_and_complete(struct ssh_packet *p, int status)
+{
+	/*
+	 * A call to this function should in general be preceeded by
+	 * set_bit(SSH_PACKET_SF_LOCKED_BIT, &p->flags) to avoid re-adding the
+	 * packet to the structures it's going to be removed from.
+	 *
+	 * The set_bit call does not need explicit memory barriers as the
+	 * implicit barrier of the test_and_set_bit call below ensure that the
+	 * flag is visible before we actually attempt to remove the packet.
+	 */
+
+	if (test_and_set_bit(SSH_PACKET_SF_COMPLETED_BIT, &p->state))
+		return;
+
+	ssh_ptl_queue_remove(p);
+	ssh_ptl_pending_remove(p);
+
+	__ssh_ptl_complete(p, status);
+}
+
+
+static bool ssh_ptl_tx_can_process(struct ssh_packet *packet)
+{
+	struct ssh_ptl *ptl = packet->ptl;
+
+	if (test_bit(SSH_PACKET_TY_FLUSH_BIT, &packet->state))
+		return !atomic_read(&ptl->pending.count);
+
+	// we can alwas process non-blocking packets
+	if (!test_bit(SSH_PACKET_TY_BLOCKING_BIT, &packet->state))
+		return true;
+
+	// if we are already waiting for this packet, send it again
+	if (test_bit(SSH_PACKET_SF_PENDING_BIT, &packet->state))
+		return true;
+
+	// otherwise: check if we have the capacity to send
+	return atomic_read(&ptl->pending.count) < SSH_PTL_MAX_PENDING;
+}
+
+static struct ssh_packet *ssh_ptl_tx_pop(struct ssh_ptl *ptl)
+{
+	struct ssh_packet *packet = ERR_PTR(-ENOENT);
+	struct ssh_packet *p, *n;
+
+	spin_lock(&ptl->queue.lock);
+	list_for_each_entry_safe(p, n, &ptl->queue.head, queue_node) {
+		/*
+		 * If we are cancelling or completing this packet, ignore it.
+		 * It's going to be removed from this queue shortly.
+		 */
+		if (test_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state))
+			continue;
+
+		/*
+		 * Packets should be ordered non-blocking/to-be-resent first.
+		 * If we cannot process this packet, assume that we can't
+		 * process any following packet either and abort.
+		 */
+		if (!ssh_ptl_tx_can_process(p)) {
+			packet = ERR_PTR(-EBUSY);
+			break;
+		}
+
+		/*
+		 * We are allowed to change the state now. Remove it from the
+		 * queue and mark it as being transmitted. Note that we cannot
+		 * add it to the set of pending packets yet, as queue locks must
+		 * always be acquired before packet locks (otherwise we might
+		 * run into a deadlock).
+		 */
+
+		list_del(&p->queue_node);
+
+		/*
+		 * Ensure that the "queued" bit gets cleared after setting the
+		 * "transmitting" bit to guaranteee non-zero flags.
+		 */
+		set_bit(SSH_PACKET_SF_TRANSMITTING_BIT, &p->state);
+		smp_mb__before_atomic();
+		clear_bit(SSH_PACKET_SF_QUEUED_BIT, &p->state);
+
+		packet = p;
+		break;
+	}
+	spin_unlock(&ptl->queue.lock);
+
+	return packet;
+}
+
+static struct ssh_packet *ssh_ptl_tx_next(struct ssh_ptl *ptl)
+{
+	struct ssh_packet *p;
+
+	p = ssh_ptl_tx_pop(ptl);
+	if (IS_ERR(p))
+		return p;
+
+	if (test_bit(SSH_PACKET_TY_SEQUENCED_BIT, &p->state)) {
+		ptl_dbg(ptl, "ptl: transmitting sequenced packet %p\n", p);
+		ssh_ptl_pending_push(p);
+		ssh_ptl_timeout_start(p);
+	} else {
+		ptl_dbg(ptl, "ptl: transmitting non-sequenced packet %p\n", p);
+	}
+
+	/*
+	 * Update number of tries. This directly influences the priority in case
+	 * the packet is re-submitted (e.g. via timeout/NAK). Note that this is
+	 * the only place where we update the priority in-flight. As this runs
+	 * only on the tx-thread, this read-modify-write procedure is safe.
+	 */
+	WRITE_ONCE(p->priority, READ_ONCE(p->priority) + 1);
+
+	return p;
+}
+
+static void ssh_ptl_tx_compl_success(struct ssh_packet *packet)
+{
+	struct ssh_ptl *ptl = packet->ptl;
+
+	ptl_dbg(ptl, "ptl: successfully transmitted packet %p\n", packet);
+
+	/*
+	 * Transition to state to "transmitted". Ensure that the flags never get
+	 * zero with barrier.
+	 */
+	set_bit(SSH_PACKET_SF_TRANSMITTED_BIT, &packet->state);
+	smp_mb__before_atomic();
+	clear_bit(SSH_PACKET_SF_TRANSMITTING_BIT, &packet->state);
+
+	// if the packet is unsequenced, we're done: lock and complete
+	if (!test_bit(SSH_PACKET_TY_SEQUENCED_BIT, &packet->state)) {
+		set_bit(SSH_PACKET_SF_LOCKED_BIT, &packet->state);
+		ssh_ptl_remove_and_complete(packet, 0);
+	}
+
+	/*
+	 * Notify that a packet transmission has finished. In general we're only
+	 * waiting for one packet (if any), so wake_up_all should be fine.
+	 */
+	wake_up_all(&ptl->tx.packet_wq);
+}
+
+static void ssh_ptl_tx_compl_error(struct ssh_packet *packet, int status)
+{
+	/*
+	 * Transmission failure: Lock the packet and try to complete it. Ensure
+	 * that the flags never get zero with barrier.
+	 */
+	set_bit(SSH_PACKET_SF_LOCKED_BIT, &packet->state);
+	smp_mb__before_atomic();
+	clear_bit(SSH_PACKET_SF_TRANSMITTING_BIT, &packet->state);
+
+	ptl_err(packet->ptl, "ptl: transmission error: %d\n", status);
+	ptl_dbg(packet->ptl, "ptl: failed to transmit packet: %p\n", packet);
+
+	ssh_ptl_remove_and_complete(packet, status);
+
+	/*
+	 * Notify that a packet transmission has finished. In general we're only
+	 * waiting for one packet (if any), so wake_up_all should be fine.
+	 */
+	wake_up_all(&packet->ptl->tx.packet_wq);
+}
+
+static void ssh_ptl_tx_threadfn_wait(struct ssh_ptl *ptl)
+{
+	wait_event_interruptible(ptl->tx.thread_wq,
+		READ_ONCE(ptl->tx.thread_signal) || kthread_should_stop());
+	WRITE_ONCE(ptl->tx.thread_signal, false);
+}
+
+static int ssh_ptl_tx_threadfn(void *data)
+{
+	struct ssh_ptl *ptl = data;
+
+	while (!kthread_should_stop()) {
+		unsigned char *buf;
+		bool drop = false;
+		size_t len = 0;
+		int status = 0;
+
+		// if we don't have a packet, get the next and add it to pending
+		if (IS_ERR_OR_NULL(ptl->tx.packet)) {
+			ptl->tx.packet = ssh_ptl_tx_next(ptl);
+			ptl->tx.offset = 0;
+
+			// if no packet is available, we are done
+			if (IS_ERR(ptl->tx.packet)) {
+				ssh_ptl_tx_threadfn_wait(ptl);
+				continue;
+			}
+		}
+
+		// error injection: drop packet to simulate transmission problem
+		if (ptl->tx.offset == 0)
+			drop = ssh_ptl_should_drop_packet(ptl->tx.packet);
+
+		// error injection: simulate invalid packet data
+		if (ptl->tx.offset == 0 && !drop)
+			ssh_ptl_tx_inject_invalid_data(ptl->tx.packet);
+
+		// flush-packets don't have any data
+		if (likely(ptl->tx.packet->data.ptr && !drop)) {
+			buf = ptl->tx.packet->data.ptr + ptl->tx.offset;
+			len = ptl->tx.packet->data.len - ptl->tx.offset;
+
+			ptl_dbg(ptl, "tx: sending data (length: %zu)\n", len);
+			print_hex_dump_debug("tx: ", DUMP_PREFIX_OFFSET, 16, 1,
+					     buf, len, false);
+
+			status = ssh_ptl_write_buf(ptl, ptl->tx.packet, buf, len);
+		}
+
+		if (status < 0) {
+			// complete packet with error
+			ssh_ptl_tx_compl_error(ptl->tx.packet, status);
+			ssh_packet_put(ptl->tx.packet);
+			ptl->tx.packet = NULL;
+
+		} else if (status == len) {
+			// complete packet and/or mark as transmitted
+			ssh_ptl_tx_compl_success(ptl->tx.packet);
+			ssh_packet_put(ptl->tx.packet);
+			ptl->tx.packet = NULL;
+
+		} else {	// need more buffer space
+			ptl->tx.offset += status;
+			ssh_ptl_tx_threadfn_wait(ptl);
+		}
+	}
+
+	// cancel active packet before we actually stop
+	if (!IS_ERR_OR_NULL(ptl->tx.packet)) {
+		ssh_ptl_tx_compl_error(ptl->tx.packet, -ESHUTDOWN);
+		ssh_packet_put(ptl->tx.packet);
+		ptl->tx.packet = NULL;
+	}
+
+	return 0;
+}
+
+static inline void ssh_ptl_tx_wakeup(struct ssh_ptl *ptl, bool force)
+{
+	if (test_bit(SSH_PTL_SF_SHUTDOWN_BIT, &ptl->state))
+		return;
+
+	if (force || atomic_read(&ptl->pending.count) < SSH_PTL_MAX_PENDING) {
+		WRITE_ONCE(ptl->tx.thread_signal, true);
+		smp_mb__after_atomic();
+		wake_up(&ptl->tx.thread_wq);
+	}
+}
+
+static int ssh_ptl_tx_start(struct ssh_ptl *ptl)
+{
+	ptl->tx.thread = kthread_run(ssh_ptl_tx_threadfn, ptl, "surface-sh-tx");
+	if (IS_ERR(ptl->tx.thread))
+		return PTR_ERR(ptl->tx.thread);
+
+	return 0;
+}
+
+static int ssh_ptl_tx_stop(struct ssh_ptl *ptl)
+{
+	int status = 0;
+
+	if (ptl->tx.thread) {
+		status = kthread_stop(ptl->tx.thread);
+		ptl->tx.thread = NULL;
+	}
+
+	return status;
+}
+
+
+static struct ssh_packet *ssh_ptl_ack_pop(struct ssh_ptl *ptl, u8 seq_id)
+{
+	struct ssh_packet *packet = ERR_PTR(-ENOENT);
+	struct ssh_packet *p, *n;
+
+	spin_lock(&ptl->pending.lock);
+	list_for_each_entry_safe(p, n, &ptl->pending.head, pending_node) {
+		/*
+		 * We generally expect packets to be in order, so first packet
+		 * to be added to pending is first to be sent, is first to be
+		 * ACKed.
+		 */
+		if (unlikely(ssh_packet_get_seq(p) != seq_id))
+			continue;
+
+		/*
+		 * In case we receive an ACK while handling a transmission error
+		 * completion. The packet will be removed shortly.
+		 */
+		if (unlikely(test_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state))) {
+			packet = ERR_PTR(-EPERM);
+			break;
+		}
+
+		/*
+		 * Mark packet as ACKed and remove it from pending. Ensure that
+		 * the flags never get zero with barrier.
+		 */
+		set_bit(SSH_PACKET_SF_ACKED_BIT, &p->state);
+		smp_mb__before_atomic();
+		clear_bit(SSH_PACKET_SF_PENDING_BIT, &p->state);
+
+		atomic_dec(&ptl->pending.count);
+		list_del(&p->pending_node);
+		packet = p;
+
+		break;
+	}
+	spin_unlock(&ptl->pending.lock);
+
+	return packet;
+}
+
+static void ssh_ptl_wait_until_transmitted(struct ssh_packet *packet)
+{
+	wait_event(packet->ptl->tx.packet_wq,
+		   test_bit(SSH_PACKET_SF_TRANSMITTED_BIT, &packet->state)
+		   || test_bit(SSH_PACKET_SF_LOCKED_BIT, &packet->state));
+}
+
+static void ssh_ptl_acknowledge(struct ssh_ptl *ptl, u8 seq)
+{
+	struct ssh_packet *p;
+	int status = 0;
+
+	p = ssh_ptl_ack_pop(ptl, seq);
+	if (IS_ERR(p)) {
+		if (PTR_ERR(p) == -ENOENT) {
+			/*
+			 * The packet has not been found in the set of pending
+			 * packets.
+			 */
+			ptl_warn(ptl, "ptl: received ACK for non-pending"
+				 " packet\n");
+		} else {
+			/*
+			 * The packet is pending, but we are not allowed to take
+			 * it because it has been locked.
+			 */
+		}
+		return;
+	}
+
+	ptl_dbg(ptl, "ptl: received ACK for packet %p\n", p);
+
+	/*
+	 * It is possible that the packet has been transmitted, but the state
+	 * has not been updated from "transmitting" to "transmitted" yet.
+	 * In that case, we need to wait for this transition to occur in order
+	 * to determine between success or failure.
+	 */
+	if (test_bit(SSH_PACKET_SF_TRANSMITTING_BIT, &p->state))
+		ssh_ptl_wait_until_transmitted(p);
+
+	/*
+	 * The packet will already be locked in case of a transmission error or
+	 * cancellation. Let the transmitter or cancellation issuer complete the
+	 * packet.
+	 */
+	if (unlikely(test_and_set_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state))) {
+		ssh_packet_put(p);
+		return;
+	}
+
+	if (unlikely(!test_bit(SSH_PACKET_SF_TRANSMITTED_BIT, &p->state))) {
+		ptl_err(ptl, "ptl: received ACK before packet had been fully"
+			" transmitted\n");
+		status = -EREMOTEIO;
+	}
+
+	ssh_ptl_remove_and_complete(p, status);
+	ssh_packet_put(p);
+
+	ssh_ptl_tx_wakeup(ptl, false);
+}
+
+
+static int ssh_ptl_submit(struct ssh_ptl *ptl, struct ssh_packet *p)
+{
+	struct ssh_ptl *ptl_old;
+	int status;
+
+	trace_ssam_packet_submit(p);
+
+	// validate packet fields
+	if (test_bit(SSH_PACKET_TY_FLUSH_BIT, &p->state)) {
+		if (p->data.ptr || test_bit(SSH_PACKET_TY_SEQUENCED_BIT, &p->state))
+			return -EINVAL;
+	} else if (!p->data.ptr) {
+		return -EINVAL;
+	}
+
+	/*
+	 * The ptl reference only gets set on or before the first submission.
+	 * After the first submission, it has to be read-only.
+	 */
+	ptl_old = READ_ONCE(p->ptl);
+	if (ptl_old == NULL)
+		WRITE_ONCE(p->ptl, ptl);
+	else if (ptl_old != ptl)
+		return -EALREADY;
+
+	status = ssh_ptl_queue_push(p);
+	if (status)
+		return status;
+
+	ssh_ptl_tx_wakeup(ptl, !test_bit(SSH_PACKET_TY_BLOCKING_BIT, &p->state));
+	return 0;
+}
+
+static void __ssh_ptl_resubmit(struct ssh_packet *packet)
+{
+	struct list_head *head;
+
+	trace_ssam_packet_resubmit(packet);
+
+	spin_lock(&packet->ptl->queue.lock);
+
+	// if this packet has already been queued, do not add it
+	if (test_and_set_bit(SSH_PACKET_SF_QUEUED_BIT, &packet->state)) {
+		spin_unlock(&packet->ptl->queue.lock);
+		return;
+	}
+
+	// find first node with lower priority
+	head = __ssh_ptl_queue_find_entrypoint(packet);
+
+	WRITE_ONCE(packet->timestamp, KTIME_MAX);
+	smp_mb__after_atomic();
+
+	// add packet
+	ssh_packet_get(packet);
+	list_add_tail(&packet->queue_node, head);
+
+	spin_unlock(&packet->ptl->queue.lock);
+}
+
+static void ssh_ptl_resubmit_pending(struct ssh_ptl *ptl)
+{
+	struct ssh_packet *p;
+	bool resub = false;
+	u8 try;
+
+	/*
+	 * Note: We deliberately do not remove/attempt to cancel and complete
+	 * packets that are out of tires in this function. The packet will be
+	 * eventually canceled and completed by the timeout. Removing the packet
+	 * here could lead to overly eager cancelation if the packet has not
+	 * been re-transmitted yet but the tries-counter already updated (i.e
+	 * ssh_ptl_tx_next removed the packet from the queue and updated the
+	 * counter, but re-transmission for the last try has not actually
+	 * started yet).
+	 */
+
+	spin_lock(&ptl->pending.lock);
+
+	// re-queue all pending packets
+	list_for_each_entry(p, &ptl->pending.head, pending_node) {
+		// avoid further transitions if locked
+		if (test_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state))
+			continue;
+
+		// do not re-schedule if packet is out of tries
+		try = ssh_packet_priority_get_try(READ_ONCE(p->priority));
+		if (try >= SSH_PTL_MAX_PACKET_TRIES)
+			continue;
+
+		resub = true;
+		__ssh_ptl_resubmit(p);
+	}
+
+	spin_unlock(&ptl->pending.lock);
+
+	ssh_ptl_tx_wakeup(ptl, resub);
+}
+
+static void ssh_ptl_cancel(struct ssh_packet *p)
+{
+	if (test_and_set_bit(SSH_PACKET_SF_CANCELED_BIT, &p->state))
+		return;
+
+	trace_ssam_packet_cancel(p);
+
+	/*
+	 * Lock packet and commit with memory barrier. If this packet has
+	 * already been locked, it's going to be removed and completed by
+	 * another party, which should have precedence.
+	 */
+	if (test_and_set_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state))
+		return;
+
+	/*
+	 * By marking the packet as locked and employing the implicit memory
+	 * barrier of test_and_set_bit, we have guaranteed that, at this point,
+	 * the packet cannot be added to the queue any more.
+	 *
+	 * In case the packet has never been submitted, packet->ptl is NULL. If
+	 * the packet is currently being submitted, packet->ptl may be NULL or
+	 * non-NULL. Due marking the packet as locked above and committing with
+	 * the memory barrier, we have guaranteed that, if packet->ptl is NULL,
+	 * the packet will never be added to the queue. If packet->ptl is
+	 * non-NULL, we don't have any guarantees.
+	 */
+
+	if (READ_ONCE(p->ptl)) {
+		ssh_ptl_remove_and_complete(p, -ECANCELED);
+		ssh_ptl_tx_wakeup(p->ptl, false);
+	} else if (!test_and_set_bit(SSH_PACKET_SF_COMPLETED_BIT, &p->state)) {
+		__ssh_ptl_complete(p, -ECANCELED);
+	}
+}
+
+
+static ktime_t ssh_packet_get_expiration(struct ssh_packet *p, ktime_t timeout)
+{
+	ktime_t timestamp = READ_ONCE(p->timestamp);
+
+	if (timestamp != KTIME_MAX)
+		return ktime_add(timestamp, timeout);
+	else
+		return KTIME_MAX;
+}
+
+static void ssh_ptl_timeout_reap(struct work_struct *work)
+{
+	struct ssh_ptl *ptl = to_ssh_ptl(work, rtx_timeout.reaper.work);
+	struct ssh_packet *p, *n;
+	LIST_HEAD(claimed);
+	ktime_t now = ktime_get_coarse_boottime();
+	ktime_t timeout = ptl->rtx_timeout.timeout;
+	ktime_t next = KTIME_MAX;
+	bool resub = false;
+
+	trace_ssam_ptl_timeout_reap("pending", atomic_read(&ptl->pending.count));
+
+	/*
+	 * Mark reaper as "not pending". This is done before checking any
+	 * packets to avoid lost-update type problems.
+	 */
+	WRITE_ONCE(ptl->rtx_timeout.expires, KTIME_MAX);
+	smp_mb__after_atomic();
+
+	spin_lock(&ptl->pending.lock);
+
+	list_for_each_entry_safe(p, n, &ptl->pending.head, pending_node) {
+		ktime_t expires = ssh_packet_get_expiration(p, timeout);
+		u8 try;
+
+		/*
+		 * Check if the timeout hasn't expired yet. Find out next
+		 * expiration date to be handled after this run.
+		 */
+		if (ktime_after(expires, now)) {
+			next = ktime_before(expires, next) ? expires : next;
+			continue;
+		}
+
+		// avoid further transitions if locked
+		if (test_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state))
+			continue;
+
+		trace_ssam_packet_timeout(p);
+
+		// check if we still have some tries left
+		try = ssh_packet_priority_get_try(READ_ONCE(p->priority));
+		if (likely(try < SSH_PTL_MAX_PACKET_TRIES)) {
+			resub = true;
+			__ssh_ptl_resubmit(p);
+			continue;
+		}
+
+		// no more tries left: cancel the packet
+
+		// if someone else has locked the packet already, don't use it
+		if (test_and_set_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state))
+			continue;
+
+		/*
+		 * We have now marked the packet as locked. Thus it cannot be
+		 * added to the pending list again after we've removed it here.
+		 * We can therefore re-use the pending_node of this packet
+		 * temporarily.
+		 */
+
+		clear_bit(SSH_PACKET_SF_PENDING_BIT, &p->state);
+
+		atomic_dec(&ptl->pending.count);
+		list_del(&p->pending_node);
+
+		list_add_tail(&p->pending_node, &claimed);
+	}
+
+	spin_unlock(&ptl->pending.lock);
+
+	// cancel and complete the packet
+	list_for_each_entry_safe(p, n, &claimed, pending_node) {
+		if (!test_and_set_bit(SSH_PACKET_SF_COMPLETED_BIT, &p->state)) {
+			ssh_ptl_queue_remove(p);
+			__ssh_ptl_complete(p, -ETIMEDOUT);
+		}
+
+		// drop the reference we've obtained by removing it from pending
+		list_del(&p->pending_node);
+		ssh_packet_put(p);
+	}
+
+	// ensure that reaper doesn't run again immediately
+	next = max(next, ktime_add(now, SSH_PTL_PACKET_TIMEOUT_RESOLUTION));
+	if (next != KTIME_MAX)
+		ssh_ptl_timeout_reaper_mod(ptl, now, next);
+
+	// force-wakeup to properly handle re-transmits if we've re-submitted
+	ssh_ptl_tx_wakeup(ptl, resub);
+}
+
+
+static bool ssh_ptl_rx_retransmit_check(struct ssh_ptl *ptl, u8 seq)
+{
+	int i;
+
+	// check if SEQ has been seen recently (i.e. packet was re-transmitted)
+	for (i = 0; i < ARRAY_SIZE(ptl->rx.blocked.seqs); i++) {
+		if (likely(ptl->rx.blocked.seqs[i] != seq))
+			continue;
+
+		ptl_dbg(ptl, "ptl: ignoring repeated data packet\n");
+		return true;
+	}
+
+	// update list of blocked seuence IDs
+	ptl->rx.blocked.seqs[ptl->rx.blocked.offset] = seq;
+	ptl->rx.blocked.offset = (ptl->rx.blocked.offset + 1)
+				  % ARRAY_SIZE(ptl->rx.blocked.seqs);
+
+	return false;
+}
+
+static void ssh_ptl_rx_dataframe(struct ssh_ptl *ptl,
+				 const struct ssh_frame *frame,
+				 const struct ssam_span *payload)
+{
+	if (ssh_ptl_rx_retransmit_check(ptl, frame->seq))
+		return;
+
+	ptl->ops.data_received(ptl, payload);
+}
+
+static void ssh_ptl_send_ack(struct ssh_ptl *ptl, u8 seq)
+{
+	struct ssh_packet_args args;
+	struct ssh_packet *packet;
+	struct ssam_span buf;
+	struct msgbuf msgb;
+	int status;
+
+	status = ssh_ctrl_packet_alloc(&packet, &buf, GFP_KERNEL);
+	if (status) {
+		ptl_err(ptl, "ptl: failed to allocate ACK packet\n");
+		return;
+	}
+
+	args.type = 0;
+	args.priority = SSH_PACKET_PRIORITY(ACK, 0);
+	args.ops = &ssh_ptl_ctrl_packet_ops;
+	ssh_packet_init(packet, &args);
+
+	msgb_init(&msgb, buf.ptr, buf.len);
+	msgb_push_ack(&msgb, seq);
+	ssh_packet_set_data(packet, msgb.begin, msgb_bytes_used(&msgb));
+
+	ssh_ptl_submit(ptl, packet);
+	ssh_packet_put(packet);
+}
+
+static void ssh_ptl_send_nak(struct ssh_ptl *ptl)
+{
+	struct ssh_packet_args args;
+	struct ssh_packet *packet;
+	struct ssam_span buf;
+	struct msgbuf msgb;
+	int status;
+
+	status = ssh_ctrl_packet_alloc(&packet, &buf, GFP_KERNEL);
+	if (status) {
+		ptl_err(ptl, "ptl: failed to allocate NAK packet\n");
+		return;
+	}
+
+	args.type = 0;
+	args.priority = SSH_PACKET_PRIORITY(NAK, 0);
+	args.ops = &ssh_ptl_ctrl_packet_ops;
+	ssh_packet_init(packet, &args);
+
+	msgb_init(&msgb, buf.ptr, buf.len);
+	msgb_push_nak(&msgb);
+	ssh_packet_set_data(packet, msgb.begin, msgb_bytes_used(&msgb));
+
+	ssh_ptl_submit(ptl, packet);
+	ssh_packet_put(packet);
+}
+
+static size_t ssh_ptl_rx_eval(struct ssh_ptl *ptl, struct ssam_span *source)
+{
+	struct ssh_frame *frame;
+	struct ssam_span payload;
+	struct ssam_span aligned;
+	bool syn_found;
+	int status;
+
+	// error injection: modify data to simulate corrupt SYN bytes
+	ssh_ptl_rx_inject_invalid_syn(ptl, source);
+
+	// find SYN
+	syn_found = sshp_find_syn(source, &aligned);
+
+	if (unlikely(aligned.ptr - source->ptr) > 0) {
+		ptl_warn(ptl, "rx: parser: invalid start of frame, skipping\n");
+
+		/*
+		 * Notes:
+		 * - This might send multiple NAKs in case the communication
+		 *   starts with an invalid SYN and is broken down into multiple
+		 *   pieces. This should generally be handled fine, we just
+		 *   might receive duplicate data in this case, which is
+		 *   detected when handling data frames.
+		 * - This path will also be executed on invalid CRCs: When an
+		 *   invalid CRC is encountered, the code below will skip data
+		 *   until direclty after the SYN. This causes the search for
+		 *   the next SYN, which is generally not placed directly after
+		 *   the last one.
+		 */
+		ssh_ptl_send_nak(ptl);
+	}
+
+	if (unlikely(!syn_found))
+		return aligned.ptr - source->ptr;
+
+	// error injection: modify data to simulate corruption
+	ssh_ptl_rx_inject_invalid_data(ptl, &aligned);
+
+	// parse and validate frame
+	status = sshp_parse_frame(&ptl->serdev->dev, &aligned, &frame, &payload,
+				  SSH_PTL_RX_BUF_LEN);
+	if (status)	// invalid frame: skip to next syn
+		return aligned.ptr - source->ptr + sizeof(u16);
+	if (!frame)	// not enough data
+		return aligned.ptr - source->ptr;
+
+	trace_ssam_rx_frame_received(frame);
+
+	switch (frame->type) {
+	case SSH_FRAME_TYPE_ACK:
+		ssh_ptl_acknowledge(ptl, frame->seq);
+		break;
+
+	case SSH_FRAME_TYPE_NAK:
+		ssh_ptl_resubmit_pending(ptl);
+		break;
+
+	case SSH_FRAME_TYPE_DATA_SEQ:
+		ssh_ptl_send_ack(ptl, frame->seq);
+		/* fallthrough */
+
+	case SSH_FRAME_TYPE_DATA_NSQ:
+		ssh_ptl_rx_dataframe(ptl, frame, &payload);
+		break;
+
+	default:
+		ptl_warn(ptl, "ptl: received frame with unknown type 0x%02x\n",
+			 frame->type);
+		break;
+	}
+
+	return aligned.ptr - source->ptr + SSH_MESSAGE_LENGTH(frame->len);
+}
+
+static int ssh_ptl_rx_threadfn(void *data)
+{
+	struct ssh_ptl *ptl = data;
+
+	while (true) {
+		struct ssam_span span;
+		size_t offs = 0;
+		size_t n;
+
+		wait_event_interruptible(ptl->rx.wq,
+					 !kfifo_is_empty(&ptl->rx.fifo)
+					 || kthread_should_stop());
+		if (kthread_should_stop())
+			break;
+
+		// copy from fifo to evaluation buffer
+		n = sshp_buf_read_from_fifo(&ptl->rx.buf, &ptl->rx.fifo);
+
+		ptl_dbg(ptl, "rx: received data (size: %zu)\n", n);
+		print_hex_dump_debug("rx: ", DUMP_PREFIX_OFFSET, 16, 1,
+				     ptl->rx.buf.ptr + ptl->rx.buf.len - n,
+				     n, false);
+
+		// parse until we need more bytes or buffer is empty
+		while (offs < ptl->rx.buf.len) {
+			sshp_buf_span_from(&ptl->rx.buf, offs, &span);
+			n = ssh_ptl_rx_eval(ptl, &span);
+			if (n == 0)
+				break;	// need more bytes
+
+			offs += n;
+		}
+
+		// throw away the evaluated parts
+		sshp_buf_drop(&ptl->rx.buf, offs);
+	}
+
+	return 0;
+}
+
+static inline void ssh_ptl_rx_wakeup(struct ssh_ptl *ptl)
+{
+	wake_up(&ptl->rx.wq);
+}
+
+static int ssh_ptl_rx_start(struct ssh_ptl *ptl)
+{
+	if (ptl->rx.thread)
+		return 0;
+
+	ptl->rx.thread = kthread_run(ssh_ptl_rx_threadfn, ptl, "surface-sh-rx");
+	if (IS_ERR(ptl->rx.thread))
+		return PTR_ERR(ptl->rx.thread);
+
+	return 0;
+}
+
+static int ssh_ptl_rx_stop(struct ssh_ptl *ptl)
+{
+	int status = 0;
+
+	if (ptl->rx.thread) {
+		status = kthread_stop(ptl->rx.thread);
+		ptl->rx.thread = NULL;
+	}
+
+	return status;
+}
+
+static int ssh_ptl_rx_rcvbuf(struct ssh_ptl *ptl, const u8 *buf, size_t n)
+{
+	int used;
+
+	if (test_bit(SSH_PTL_SF_SHUTDOWN_BIT, &ptl->state))
+		return -ESHUTDOWN;
+
+	used = kfifo_in(&ptl->rx.fifo, buf, n);
+	if (used)
+		ssh_ptl_rx_wakeup(ptl);
+
+	return used;
+}
+
+
+struct ssh_flush_packet {
+	struct ssh_packet base;
+	struct completion completion;
+	int status;
+};
+
+static void ssh_ptl_flush_complete(struct ssh_packet *p, int status)
+{
+	struct ssh_flush_packet *packet;
+
+	packet = container_of(p, struct ssh_flush_packet, base);
+	packet->status = status;
+}
+
+static void ssh_ptl_flush_release(struct ssh_packet *p)
+{
+	struct ssh_flush_packet *packet;
+
+	packet = container_of(p, struct ssh_flush_packet, base);
+	complete_all(&packet->completion);
+}
+
+static const struct ssh_packet_ops ssh_flush_packet_ops =  {
+	.complete = ssh_ptl_flush_complete,
+	.release = ssh_ptl_flush_release,
+};
+
+/**
+ * ssh_ptl_shutdown - shut down the packet transmission layer
+ * @ptl:     packet transmission layer
+ *
+ * Shuts down the packet transmission layer, removing and canceling all queued
+ * and pending packets. Packets canceled by this operation will be completed
+ * with -ESHUTDOWN as status.
+ *
+ * As a result of this function, the transmission layer will be marked as shut
+ * down. Submission of packets after the transmission layer has been shut down
+ * will fail with -ESHUTDOWN.
+ */
+static void ssh_ptl_shutdown(struct ssh_ptl *ptl)
+{
+	LIST_HEAD(complete_q);
+	LIST_HEAD(complete_p);
+	struct ssh_packet *p, *n;
+	int status;
+
+	// ensure that no new packets (including ACK/NAK) can be submitted
+	set_bit(SSH_PTL_SF_SHUTDOWN_BIT, &ptl->state);
+	smp_mb__after_atomic();
+
+	status = ssh_ptl_rx_stop(ptl);
+	if (status)
+		ptl_err(ptl, "ptl: failed to stop receiver thread\n");
+
+	status = ssh_ptl_tx_stop(ptl);
+	if (status)
+		ptl_err(ptl, "ptl: failed to stop transmitter thread\n");
+
+	cancel_delayed_work_sync(&ptl->rtx_timeout.reaper);
+
+	/*
+	 * At this point, all threads have been stopped. This means that the
+	 * only references to packets from inside the system are in the queue
+	 * and pending set.
+	 *
+	 * Note: We still need locks here because someone could still be
+	 * cancelling packets.
+	 *
+	 * Note 2: We can re-use queue_node (or pending_node) if we mark the
+	 * packet as locked an then remove it from the queue (or pending set
+	 * respecitvely). Marking the packet as locked avoids re-queueing
+	 * (which should already be prevented by having stopped the treads...)
+	 * and not setting QUEUED_BIT (or PENDING_BIT) prevents removal from a
+	 * new list via other threads (e.g. canellation).
+	 *
+	 * Note 3: There may be overlap between complete_p and complete_q.
+	 * This is handled via test_and_set_bit on the "completed" flag
+	 * (also handles cancelation).
+	 */
+
+	// mark queued packets as locked and move them to complete_q
+	spin_lock(&ptl->queue.lock);
+	list_for_each_entry_safe(p, n, &ptl->queue.head, queue_node) {
+		set_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state);
+		smp_mb__before_atomic();
+		clear_bit(SSH_PACKET_SF_QUEUED_BIT, &p->state);
+
+		list_del(&p->queue_node);
+		list_add_tail(&p->queue_node, &complete_q);
+	}
+	spin_unlock(&ptl->queue.lock);
+
+	// mark pending packets as locked and move them to complete_p
+	spin_lock(&ptl->pending.lock);
+	list_for_each_entry_safe(p, n, &ptl->pending.head, pending_node) {
+		set_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state);
+		smp_mb__before_atomic();
+		clear_bit(SSH_PACKET_SF_PENDING_BIT, &p->state);
+
+		list_del(&p->pending_node);
+		list_add_tail(&p->pending_node, &complete_q);
+	}
+	atomic_set(&ptl->pending.count, 0);
+	spin_unlock(&ptl->pending.lock);
+
+	// complete and drop packets on complete_q
+	list_for_each_entry(p, &complete_q, queue_node) {
+		if (!test_and_set_bit(SSH_PACKET_SF_COMPLETED_BIT, &p->state))
+			__ssh_ptl_complete(p, -ESHUTDOWN);
+
+		ssh_packet_put(p);
+	}
+
+	// complete and drop packets on complete_p
+	list_for_each_entry(p, &complete_p, pending_node) {
+		if (!test_and_set_bit(SSH_PACKET_SF_COMPLETED_BIT, &p->state))
+			__ssh_ptl_complete(p, -ESHUTDOWN);
+
+		ssh_packet_put(p);
+	}
+
+	/*
+	 * At this point we have guaranteed that the system doesn't reference
+	 * any packets any more.
+	 */
+}
+
+static inline struct device *ssh_ptl_get_device(struct ssh_ptl *ptl)
+{
+	return ptl->serdev ? &ptl->serdev->dev : NULL;
+}
+
+static int ssh_ptl_init(struct ssh_ptl *ptl, struct serdev_device *serdev,
+			struct ssh_ptl_ops *ops)
+{
+	int i, status;
+
+	ptl->serdev = serdev;
+	ptl->state = 0;
+
+	spin_lock_init(&ptl->queue.lock);
+	INIT_LIST_HEAD(&ptl->queue.head);
+
+	spin_lock_init(&ptl->pending.lock);
+	INIT_LIST_HEAD(&ptl->pending.head);
+	atomic_set_release(&ptl->pending.count, 0);
+
+	ptl->tx.thread = NULL;
+	ptl->tx.thread_signal = false;
+	ptl->tx.packet = NULL;
+	ptl->tx.offset = 0;
+	init_waitqueue_head(&ptl->tx.thread_wq);
+	init_waitqueue_head(&ptl->tx.packet_wq);
+
+	ptl->rx.thread = NULL;
+	init_waitqueue_head(&ptl->rx.wq);
+
+	ptl->rtx_timeout.timeout = SSH_PTL_PACKET_TIMEOUT;
+	ptl->rtx_timeout.expires = KTIME_MAX;
+	INIT_DELAYED_WORK(&ptl->rtx_timeout.reaper, ssh_ptl_timeout_reap);
+
+	ptl->ops = *ops;
+
+	// initialize list of recent/blocked SEQs with invalid sequence IDs
+	for (i = 0; i < ARRAY_SIZE(ptl->rx.blocked.seqs); i++)
+		ptl->rx.blocked.seqs[i] = 0xFFFF;
+	ptl->rx.blocked.offset = 0;
+
+	status = kfifo_alloc(&ptl->rx.fifo, SSH_PTL_RX_FIFO_LEN, GFP_KERNEL);
+	if (status)
+		return status;
+
+	status = sshp_buf_alloc(&ptl->rx.buf, SSH_PTL_RX_BUF_LEN, GFP_KERNEL);
+	if (status)
+		kfifo_free(&ptl->rx.fifo);
+
+	return status;
+}
+
+static void ssh_ptl_destroy(struct ssh_ptl *ptl)
+{
+	kfifo_free(&ptl->rx.fifo);
+	sshp_buf_free(&ptl->rx.buf);
+}
+
+
+/* -- Request transport layer (rtl). ---------------------------------------- */
+
+#define SSH_RTL_REQUEST_TIMEOUT			ms_to_ktime(3000)
+#define SSH_RTL_REQUEST_TIMEOUT_RESOLUTION	ms_to_ktime(max(2000 / HZ, 50))
+
+#define SSH_RTL_MAX_PENDING		3
+
+
+enum ssh_rtl_state_flags {
+	SSH_RTL_SF_SHUTDOWN_BIT,
+};
+
+struct ssh_rtl_ops {
+	void (*handle_event)(struct ssh_rtl *rtl, const struct ssh_command *cmd,
+			     const struct ssam_span *data);
+};
+
+struct ssh_rtl {
+	struct ssh_ptl ptl;
+	unsigned long state;
+
+	struct {
+		spinlock_t lock;
+		struct list_head head;
+	} queue;
+
+	struct {
+		spinlock_t lock;
+		struct list_head head;
+		atomic_t count;
+	} pending;
+
+	struct {
+		struct work_struct work;
+	} tx;
+
+	struct {
+		ktime_t timeout;
+		ktime_t expires;
+		struct delayed_work reaper;
+	} rtx_timeout;
+
+	struct ssh_rtl_ops ops;
+};
+
+
+#define rtl_dbg(r, fmt, ...)  ptl_dbg(&(r)->ptl, fmt, ##__VA_ARGS__)
+#define rtl_info(p, fmt, ...) ptl_info(&(p)->ptl, fmt, ##__VA_ARGS__)
+#define rtl_warn(r, fmt, ...) ptl_warn(&(r)->ptl, fmt, ##__VA_ARGS__)
+#define rtl_err(r, fmt, ...)  ptl_err(&(r)->ptl, fmt, ##__VA_ARGS__)
+#define rtl_dbg_cond(r, fmt, ...) __ssam_prcond(rtl_dbg, r, fmt, ##__VA_ARGS__)
+
+#define to_ssh_rtl(ptr, member) \
+	container_of(ptr, struct ssh_rtl, member)
+
+#define to_ssh_request(ptr, member) \
+	container_of(ptr, struct ssh_request, member)
+
+static inline struct ssh_rtl *ssh_request_rtl(struct ssh_request *rqst)
+{
+	struct ssh_ptl *ptl = READ_ONCE(rqst->packet.ptl);
+	return likely(ptl) ? to_ssh_rtl(ptl, ptl) : NULL;
+}
+
+
+/**
+ * ssh_rtl_should_drop_response - error injection hook to drop request responses
+ *
+ * Useful to cause request transmission timeouts in the driver by dropping the
+ * response to a request.
+ */
+static noinline_if_inject bool ssh_rtl_should_drop_response(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_rtl_should_drop_response, TRUE);
+
+
+static inline u16 ssh_request_get_rqid(struct ssh_request *rqst)
+{
+	return get_unaligned_le16(rqst->packet.data.ptr
+				  + SSH_MSGOFFSET_COMMAND(rqid));
+}
+
+static inline u32 ssh_request_get_rqid_safe(struct ssh_request *rqst)
+{
+	if (!rqst->packet.data.ptr)
+		return -1;
+
+	return ssh_request_get_rqid(rqst);
+}
+
+
+static void ssh_rtl_queue_remove(struct ssh_request *rqst)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+	bool remove;
+
+	spin_lock(&rtl->queue.lock);
+
+	remove = test_and_clear_bit(SSH_REQUEST_SF_QUEUED_BIT, &rqst->state);
+	if (remove)
+		list_del(&rqst->node);
+
+	spin_unlock(&rtl->queue.lock);
+
+	if (remove)
+		ssh_request_put(rqst);
+}
+
+static void ssh_rtl_pending_remove(struct ssh_request *rqst)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+	bool remove;
+
+	spin_lock(&rtl->pending.lock);
+
+	remove = test_and_clear_bit(SSH_REQUEST_SF_PENDING_BIT, &rqst->state);
+	if (remove) {
+		atomic_dec(&rtl->pending.count);
+		list_del(&rqst->node);
+	}
+
+	spin_unlock(&rtl->pending.lock);
+
+	if (remove)
+		ssh_request_put(rqst);
+}
+
+
+static void ssh_rtl_complete_with_status(struct ssh_request *rqst, int status)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+
+	trace_ssam_request_complete(rqst, status);
+
+	// rtl/ptl may not be set if we're cancelling before submitting
+	rtl_dbg_cond(rtl, "rtl: completing request (rqid: 0x%04x,"
+		     " status: %d)\n", ssh_request_get_rqid_safe(rqst), status);
+
+	if (status && status != -ECANCELED)
+		rtl_dbg_cond(rtl, "rtl: request error: %d\n", status);
+
+	rqst->ops->complete(rqst, NULL, NULL, status);
+}
+
+static void ssh_rtl_complete_with_rsp(struct ssh_request *rqst,
+				      const struct ssh_command *cmd,
+				      const struct ssam_span *data)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+
+	trace_ssam_request_complete(rqst, 0);
+
+	rtl_dbg(rtl, "rtl: completing request with response"
+		" (rqid: 0x%04x)\n", ssh_request_get_rqid(rqst));
+
+	rqst->ops->complete(rqst, cmd, data, 0);
+}
+
+
+static bool ssh_rtl_tx_can_process(struct ssh_request *rqst)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+
+	if (test_bit(SSH_REQUEST_TY_FLUSH_BIT, &rqst->state))
+		return !atomic_read(&rtl->pending.count);
+
+	return atomic_read(&rtl->pending.count) < SSH_RTL_MAX_PENDING;
+}
+
+static struct ssh_request *ssh_rtl_tx_next(struct ssh_rtl *rtl)
+{
+	struct ssh_request *rqst = ERR_PTR(-ENOENT);
+	struct ssh_request *p, *n;
+
+	spin_lock(&rtl->queue.lock);
+
+	// find first non-locked request and remove it
+	list_for_each_entry_safe(p, n, &rtl->queue.head, node) {
+		if (unlikely(test_bit(SSH_REQUEST_SF_LOCKED_BIT, &p->state)))
+			continue;
+
+		if (!ssh_rtl_tx_can_process(p)) {
+			rqst = ERR_PTR(-EBUSY);
+			break;
+		}
+
+		/*
+		 * Remove from queue and mark as transmitting. Ensure that the
+		 * state does not get zero via memory barrier.
+		 */
+		set_bit(SSH_REQUEST_SF_TRANSMITTING_BIT, &p->state);
+		smp_mb__before_atomic();
+		clear_bit(SSH_REQUEST_SF_QUEUED_BIT, &p->state);
+
+		list_del(&p->node);
+
+		rqst = p;
+		break;
+	}
+
+	spin_unlock(&rtl->queue.lock);
+	return rqst;
+}
+
+static int ssh_rtl_tx_pending_push(struct ssh_request *rqst)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+
+	spin_lock(&rtl->pending.lock);
+
+	if (test_bit(SSH_REQUEST_SF_LOCKED_BIT, &rqst->state)) {
+		spin_unlock(&rtl->pending.lock);
+		return -EINVAL;
+	}
+
+	if (test_and_set_bit(SSH_REQUEST_SF_PENDING_BIT, &rqst->state)) {
+		spin_unlock(&rtl->pending.lock);
+		return -EALREADY;
+	}
+
+	atomic_inc(&rtl->pending.count);
+	ssh_request_get(rqst);
+	list_add_tail(&rqst->node, &rtl->pending.head);
+
+	spin_unlock(&rtl->pending.lock);
+	return 0;
+}
+
+static int ssh_rtl_tx_try_process_one(struct ssh_rtl *rtl)
+{
+	struct ssh_request *rqst;
+	int status;
+
+	// get and prepare next request for transmit
+	rqst = ssh_rtl_tx_next(rtl);
+	if (IS_ERR(rqst))
+		return PTR_ERR(rqst);
+
+	// add to/mark as pending
+	status = ssh_rtl_tx_pending_push(rqst);
+	if (status) {
+		ssh_request_put(rqst);
+		return -EAGAIN;
+	}
+
+	// submit packet
+	status = ssh_ptl_submit(&rtl->ptl, &rqst->packet);
+	if (status == -ESHUTDOWN) {
+		/*
+		 * Packet has been refused due to the packet layer shutting
+		 * down. Complete it here.
+		 */
+		set_bit(SSH_REQUEST_SF_LOCKED_BIT, &rqst->state);
+		smp_mb__after_atomic();
+
+		ssh_rtl_pending_remove(rqst);
+		ssh_rtl_complete_with_status(rqst, -ESHUTDOWN);
+
+		ssh_request_put(rqst);
+		return -ESHUTDOWN;
+
+	} else if (status) {
+		/*
+		 * If submitting the packet failed and the packet layer isn't
+		 * shutting down, the packet has either been submmitted/queued
+		 * before (-EALREADY, which cannot happen as we have guaranteed
+		 * that requests cannot be re-submitted), or the packet was
+		 * marked as locked (-EINVAL). To mark the packet locked at this
+		 * stage, the request, and thus the packets itself, had to have
+		 * been canceled. Simply drop the reference. Cancellation itself
+		 * will remove it from the set of pending requests.
+		 */
+
+		WARN_ON(status != -EINVAL);
+
+		ssh_request_put(rqst);
+		return -EAGAIN;
+	}
+
+	ssh_request_put(rqst);
+	return 0;
+}
+
+static bool ssh_rtl_queue_empty(struct ssh_rtl *rtl)
+{
+	bool empty;
+
+	spin_lock(&rtl->queue.lock);
+	empty = list_empty(&rtl->queue.head);
+	spin_unlock(&rtl->queue.lock);
+
+	return empty;
+}
+
+static bool ssh_rtl_tx_schedule(struct ssh_rtl *rtl)
+{
+	if (atomic_read(&rtl->pending.count) >= SSH_RTL_MAX_PENDING)
+		return false;
+
+	if (ssh_rtl_queue_empty(rtl))
+		return false;
+
+	return schedule_work(&rtl->tx.work);
+}
+
+static void ssh_rtl_tx_work_fn(struct work_struct *work)
+{
+	struct ssh_rtl *rtl = to_ssh_rtl(work, tx.work);
+	int i, status;
+
+	/*
+	 * Try to be nice and not block the workqueue: Run a maximum of 10
+	 * tries, then re-submit if necessary. This should not be neccesary,
+	 * for normal execution, but guarantee it anyway.
+	 */
+	for (i = 0; i < 10; i++) {
+		status = ssh_rtl_tx_try_process_one(rtl);
+		if (status == -ENOENT || status == -EBUSY)
+			return;		// no more requests to process
+
+		if (status == -ESHUTDOWN) {
+			/*
+			 * Packet system shutting down. No new packets can be
+			 * transmitted. Return silently, the party initiating
+			 * the shutdown should handle the rest.
+			 */
+			return;
+		}
+
+		WARN_ON(status != 0 && status != -EAGAIN);
+	}
+
+	// out of tries, reschedule
+	ssh_rtl_tx_schedule(rtl);
+}
+
+
+static int ssh_rtl_submit(struct ssh_rtl *rtl, struct ssh_request *rqst)
+{
+	trace_ssam_request_submit(rqst);
+
+	/*
+	 * Ensure that requests expecting a response are sequenced. If this
+	 * invariant ever changes, see the comment in ssh_rtl_complete on what
+	 * is required to be changed in the code.
+	 */
+	if (test_bit(SSH_REQUEST_TY_HAS_RESPONSE_BIT, &rqst->state))
+		if (!test_bit(SSH_PACKET_TY_SEQUENCED_BIT, &rqst->packet.state))
+			return -EINVAL;
+
+	// try to set ptl and check if this request has already been submitted
+	if (cmpxchg(&rqst->packet.ptl, NULL, &rtl->ptl) != NULL)
+		return -EALREADY;
+
+	spin_lock(&rtl->queue.lock);
+
+	if (test_bit(SSH_RTL_SF_SHUTDOWN_BIT, &rtl->state)) {
+		spin_unlock(&rtl->queue.lock);
+		return -ESHUTDOWN;
+	}
+
+	if (test_bit(SSH_REQUEST_SF_LOCKED_BIT, &rqst->state)) {
+		spin_unlock(&rtl->queue.lock);
+		return -EINVAL;
+	}
+
+	ssh_request_get(rqst);
+	set_bit(SSH_REQUEST_SF_QUEUED_BIT, &rqst->state);
+	list_add_tail(&rqst->node, &rtl->queue.head);
+
+	spin_unlock(&rtl->queue.lock);
+
+	ssh_rtl_tx_schedule(rtl);
+	return 0;
+}
+
+
+static void ssh_rtl_timeout_reaper_mod(struct ssh_rtl *rtl, ktime_t now,
+				       ktime_t expires)
+{
+	unsigned long delta = msecs_to_jiffies(ktime_ms_delta(expires, now));
+	ktime_t aexp = ktime_add(expires, SSH_RTL_REQUEST_TIMEOUT_RESOLUTION);
+	ktime_t old;
+
+	// re-adjust / schedule reaper if it is above resolution delta
+	old = READ_ONCE(rtl->rtx_timeout.expires);
+	while (ktime_before(aexp, old))
+		old = cmpxchg64(&rtl->rtx_timeout.expires, old, expires);
+
+	// if we updated the reaper expiration, modify work timeout
+	if (old == expires)
+		mod_delayed_work(system_wq, &rtl->rtx_timeout.reaper, delta);
+}
+
+static void ssh_rtl_timeout_start(struct ssh_request *rqst)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+	ktime_t timestamp = ktime_get_coarse_boottime();
+	ktime_t timeout = rtl->rtx_timeout.timeout;
+
+	if (test_bit(SSH_REQUEST_SF_LOCKED_BIT, &rqst->state))
+		return;
+
+	WRITE_ONCE(rqst->timestamp, timestamp);
+	smp_mb__after_atomic();
+
+	ssh_rtl_timeout_reaper_mod(rtl, timestamp, timestamp + timeout);
+}
+
+
+static void ssh_rtl_complete(struct ssh_rtl *rtl,
+			     const struct ssh_command *command,
+			     const struct ssam_span *command_data)
+{
+	struct ssh_request *r = NULL;
+	struct ssh_request *p, *n;
+	u16 rqid = get_unaligned_le16(&command->rqid);
+
+	trace_ssam_rx_response_received(command, command_data->len);
+
+	/*
+	 * Get request from pending based on request ID and mark it as response
+	 * received and locked.
+	 */
+	spin_lock(&rtl->pending.lock);
+	list_for_each_entry_safe(p, n, &rtl->pending.head, node) {
+		// we generally expect requests to be processed in order
+		if (unlikely(ssh_request_get_rqid(p) != rqid))
+			continue;
+
+		// simulate response timeout
+		if (ssh_rtl_should_drop_response()) {
+			spin_unlock(&rtl->pending.lock);
+
+			trace_ssam_ei_rx_drop_response(p);
+			rtl_info(rtl, "request error injection: "
+				 "dropping response for request %p\n",
+				 &p->packet);
+			return;
+		}
+
+		/*
+		 * Mark as "response received" and "locked" as we're going to
+		 * complete it. Ensure that the state doesn't get zero by
+		 * employing a memory barrier.
+		 */
+		set_bit(SSH_REQUEST_SF_LOCKED_BIT, &p->state);
+		set_bit(SSH_REQUEST_SF_RSPRCVD_BIT, &p->state);
+		smp_mb__before_atomic();
+		clear_bit(SSH_REQUEST_SF_PENDING_BIT, &p->state);
+
+		atomic_dec(&rtl->pending.count);
+		list_del(&p->node);
+
+		r = p;
+		break;
+	}
+	spin_unlock(&rtl->pending.lock);
+
+	if (!r) {
+		rtl_warn(rtl, "rtl: dropping unexpected command message"
+			 " (rqid = 0x%04x)\n", rqid);
+		return;
+	}
+
+	// if the request hasn't been completed yet, we will do this now
+	if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state)) {
+		ssh_request_put(r);
+		ssh_rtl_tx_schedule(rtl);
+		return;
+	}
+
+	/*
+	 * Make sure the request has been transmitted. In case of a sequenced
+	 * request, we are guaranteed that the completion callback will run on
+	 * the receiver thread directly when the ACK for the packet has been
+	 * received. Similarly, this function is guaranteed to run on the
+	 * receiver thread. Thus we are guaranteed that if the packet has been
+	 * successfully transmitted and received an ACK, the transmitted flag
+	 * has been set and is visible here.
+	 *
+	 * We are currently not handling unsequenced packets here, as those
+	 * should never expect a response as ensured in ssh_rtl_submit. If this
+	 * ever changes, one would have to test for
+	 *
+	 * 	(r->state & (transmitting | transmitted))
+	 *
+	 * on unsequenced packets to determine if they could have been
+	 * transmitted. There are no synchronization guarantees as in the
+	 * sequenced case, since, in this case, the callback function will not
+	 * run on the same thread. Thus an exact determination is impossible.
+	 */
+	if (!test_bit(SSH_REQUEST_SF_TRANSMITTED_BIT, &r->state)) {
+		rtl_err(rtl, "rtl: received response before ACK for request"
+			" (rqid = 0x%04x)\n", rqid);
+
+		/*
+		 * NB: Timeout has already been canceled, request already been
+		 * removed from pending and marked as locked and completed. As
+		 * we receive a "false" response, the packet might still be
+		 * queued though.
+		 */
+		ssh_rtl_queue_remove(r);
+
+		ssh_rtl_complete_with_status(r, -EREMOTEIO);
+		ssh_request_put(r);
+
+		ssh_rtl_tx_schedule(rtl);
+		return;
+	}
+
+	/*
+	 * NB: Timeout has already been canceled, request already been
+	 * removed from pending and marked as locked and completed. The request
+	 * can also not be queued any more, as it has been marked as
+	 * transmitting and later transmitted. Thus no need to remove it from
+	 * anywhere.
+	 */
+
+	ssh_rtl_complete_with_rsp(r, command, command_data);
+	ssh_request_put(r);
+
+	ssh_rtl_tx_schedule(rtl);
+}
+
+
+static bool ssh_rtl_cancel_nonpending(struct ssh_request *r)
+{
+	struct ssh_rtl *rtl;
+	unsigned long state, fixed;
+	bool remove;
+
+	/*
+	 * Handle unsubmitted request: Try to mark the packet as locked,
+	 * expecting the state to be zero (i.e. unsubmitted). Note that, if
+	 * setting the state worked, we might still be adding the packet to the
+	 * queue in a currently executing submit call. In that case, however,
+	 * ptl reference must have been set previously, as locked is checked
+	 * after setting ptl. Thus only if we successfully lock this request and
+	 * ptl is NULL, we have successfully removed the request.
+	 * Otherwise we need to try and grab it from the queue.
+	 *
+	 * Note that if the CMPXCHG fails, we are guaranteed that ptl has
+	 * been set and is non-NULL, as states can only be nonzero after this
+	 * has been set. Also note that we need to fetch the static (type) flags
+         * to ensure that they don't cause the cmpxchg to fail.
+	 */
+        fixed = READ_ONCE(r->state) & SSH_REQUEST_FLAGS_TY_MASK;
+	state = cmpxchg(&r->state, fixed, SSH_REQUEST_SF_LOCKED_BIT);
+	if (!state && !READ_ONCE(r->packet.ptl)) {
+		if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+			return true;
+
+		ssh_rtl_complete_with_status(r, -ECANCELED);
+		return true;
+	}
+
+	rtl = ssh_request_rtl(r);
+	spin_lock(&rtl->queue.lock);
+
+	/*
+	 * Note: 1) Requests cannot be re-submitted. 2) If a request is queued,
+	 * it cannot be "transmitting"/"pending" yet. Thus, if we successfully
+	 * remove the the request here, we have removed all its occurences in
+	 * the system.
+	 */
+
+	remove = test_and_clear_bit(SSH_REQUEST_SF_QUEUED_BIT, &r->state);
+	if (!remove) {
+		spin_unlock(&rtl->queue.lock);
+		return false;
+	}
+
+	set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state);
+	list_del(&r->node);
+
+	spin_unlock(&rtl->queue.lock);
+
+	ssh_request_put(r);	// drop reference obtained from queue
+
+	if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+		return true;
+
+	ssh_rtl_complete_with_status(r, -ECANCELED);
+	return true;
+}
+
+static bool ssh_rtl_cancel_pending(struct ssh_request *r)
+{
+	// if the packet is already locked, it's going to be removed shortly
+	if (test_and_set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state))
+		return true;
+
+	/*
+	 * Now that we have locked the packet, we have guaranteed that it can't
+	 * be added to the system any more. If rtl is zero, the locked
+	 * check in ssh_rtl_submit has not been run and any submission,
+	 * currently in progress or called later, won't add the packet. Thus we
+	 * can directly complete it.
+	 */
+	if (!ssh_request_rtl(r)) {
+		if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+			return true;
+
+		ssh_rtl_complete_with_status(r, -ECANCELED);
+		return true;
+	}
+
+	/*
+	 * Try to cancel the packet. If the packet has not been completed yet,
+	 * this will subsequently (and synchronously) call the completion
+	 * callback of the packet, which will complete the request.
+	 */
+	ssh_ptl_cancel(&r->packet);
+
+	/*
+	 * If the packet has been completed with success, i.e. has not been
+	 * canceled by the above call, the request may not have been completed
+	 * yet (may be waiting for a response). Check if we need to do this
+	 * here.
+	 */
+	if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+		return true;
+
+	ssh_rtl_queue_remove(r);
+	ssh_rtl_pending_remove(r);
+	ssh_rtl_complete_with_status(r, -ECANCELED);
+
+	return true;
+}
+
+static bool ssh_rtl_cancel(struct ssh_request *rqst, bool pending)
+{
+	struct ssh_rtl *rtl;
+	bool canceled;
+
+	if (test_and_set_bit(SSH_REQUEST_SF_CANCELED_BIT, &rqst->state))
+		return true;
+
+	trace_ssam_request_cancel(rqst);
+
+	if (pending)
+		canceled = ssh_rtl_cancel_pending(rqst);
+	else
+		canceled = ssh_rtl_cancel_nonpending(rqst);
+
+	// note: rtl may be NULL if request has not been submitted yet
+	rtl = ssh_request_rtl(rqst);
+	if (canceled && rtl)
+		ssh_rtl_tx_schedule(rtl);
+
+	return canceled;
+}
+
+
+static void ssh_rtl_packet_callback(struct ssh_packet *p, int status)
+{
+	struct ssh_request *r = to_ssh_request(p, packet);
+
+	if (unlikely(status)) {
+		set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state);
+
+		if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+			return;
+
+		/*
+		 * The packet may get cancelled even though it has not been
+		 * submitted yet. The request may still be queued. Check the
+		 * queue and remove it if necessary. As the timeout would have
+		 * been started in this function on success, there's no need to
+		 * cancel it here.
+		 */
+		ssh_rtl_queue_remove(r);
+		ssh_rtl_pending_remove(r);
+		ssh_rtl_complete_with_status(r, status);
+
+		ssh_rtl_tx_schedule(ssh_request_rtl(r));
+		return;
+	}
+
+	/*
+	 * Mark as transmitted, ensure that state doesn't get zero by inserting
+	 * a memory barrier.
+	 */
+	set_bit(SSH_REQUEST_SF_TRANSMITTED_BIT, &r->state);
+	smp_mb__before_atomic();
+	clear_bit(SSH_REQUEST_SF_TRANSMITTING_BIT, &r->state);
+
+	// if we expect a response, we just need to start the timeout
+	if (test_bit(SSH_REQUEST_TY_HAS_RESPONSE_BIT, &r->state)) {
+		ssh_rtl_timeout_start(r);
+		return;
+	}
+
+	/*
+	 * If we don't expect a response, lock, remove, and complete the
+	 * request. Note that, at this point, the request is guaranteed to have
+	 * left the queue and no timeout has been started. Thus we only need to
+	 * remove it from pending. If the request has already been completed (it
+	 * may have been canceled) return.
+	 */
+
+	set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state);
+	if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+		return;
+
+	ssh_rtl_pending_remove(r);
+	ssh_rtl_complete_with_status(r, 0);
+
+	ssh_rtl_tx_schedule(ssh_request_rtl(r));
+}
+
+
+static ktime_t ssh_request_get_expiration(struct ssh_request *r, ktime_t timeo)
+{
+	ktime_t timestamp = READ_ONCE(r->timestamp);
+
+	if (timestamp != KTIME_MAX)
+		return ktime_add(timestamp, timeo);
+	else
+		return KTIME_MAX;
+}
+
+static void ssh_rtl_timeout_reap(struct work_struct *work)
+{
+	struct ssh_rtl *rtl = to_ssh_rtl(work, rtx_timeout.reaper.work);
+	struct ssh_request *r, *n;
+	LIST_HEAD(claimed);
+	ktime_t now = ktime_get_coarse_boottime();
+	ktime_t timeout = rtl->rtx_timeout.timeout;
+	ktime_t next = KTIME_MAX;
+
+	trace_ssam_rtl_timeout_reap("pending", atomic_read(&rtl->pending.count));
+
+	/*
+	 * Mark reaper as "not pending". This is done before checking any
+	 * requests to avoid lost-update type problems.
+	 */
+	WRITE_ONCE(rtl->rtx_timeout.expires, KTIME_MAX);
+	smp_mb__after_atomic();
+
+	spin_lock(&rtl->pending.lock);
+	list_for_each_entry_safe(r, n, &rtl->pending.head, node) {
+		ktime_t expires = ssh_request_get_expiration(r, timeout);
+
+		/*
+		 * Check if the timeout hasn't expired yet. Find out next
+		 * expiration date to be handled after this run.
+		 */
+		if (ktime_after(expires, now)) {
+			next = ktime_before(expires, next) ? expires : next;
+			continue;
+		}
+
+		// avoid further transitions if locked
+		if (test_and_set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state))
+			continue;
+
+		/*
+		 * We have now marked the packet as locked. Thus it cannot be
+		 * added to the pending or queued lists again after we've
+		 * removed it here. We can therefore re-use the node of this
+		 * packet temporarily.
+		 */
+
+		clear_bit(SSH_REQUEST_SF_PENDING_BIT, &r->state);
+
+		atomic_dec(&rtl->pending.count);
+		list_del(&r->node);
+
+		list_add_tail(&r->node, &claimed);
+	}
+	spin_unlock(&rtl->pending.lock);
+
+	// cancel and complete the request
+	list_for_each_entry_safe(r, n, &claimed, node) {
+		trace_ssam_request_timeout(r);
+
+		/*
+		 * At this point we've removed the packet from pending. This
+		 * means that we've obtained the last (only) reference of the
+		 * system to it. Thus we can just complete it.
+		 */
+		if (!test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+			ssh_rtl_complete_with_status(r, -ETIMEDOUT);
+
+		// drop the reference we've obtained by removing it from pending
+		list_del(&r->node);
+		ssh_request_put(r);
+	}
+
+	// ensure that reaper doesn't run again immediately
+	next = max(next, ktime_add(now, SSH_RTL_REQUEST_TIMEOUT_RESOLUTION));
+	if (next != KTIME_MAX)
+		ssh_rtl_timeout_reaper_mod(rtl, now, next);
+
+	ssh_rtl_tx_schedule(rtl);
+}
+
+
+static void ssh_rtl_rx_event(struct ssh_rtl *rtl, const struct ssh_command *cmd,
+			     const struct ssam_span *data)
+{
+	trace_ssam_rx_event_received(cmd, data->len);
+
+	rtl_dbg(rtl, "rtl: handling event (rqid: 0x%04x)\n",
+		get_unaligned_le16(&cmd->rqid));
+
+	rtl->ops.handle_event(rtl, cmd, data);
+}
+
+static void ssh_rtl_rx_command(struct ssh_ptl *p, const struct ssam_span *data)
+{
+	struct ssh_rtl *rtl = to_ssh_rtl(p, ptl);
+	struct device *dev = &p->serdev->dev;
+	struct ssh_command *command;
+	struct ssam_span command_data;
+
+	if (sshp_parse_command(dev, data, &command, &command_data))
+		return;
+
+	if (ssh_rqid_is_event(get_unaligned_le16(&command->rqid)))
+		ssh_rtl_rx_event(rtl, command, &command_data);
+	else
+		ssh_rtl_complete(rtl, command, &command_data);
+}
+
+static void ssh_rtl_rx_data(struct ssh_ptl *p, const struct ssam_span *data)
+{
+	switch (data->ptr[0]) {
+	case SSH_PLD_TYPE_CMD:
+		ssh_rtl_rx_command(p, data);
+		break;
+
+	default:
+		ptl_err(p, "rtl: rx: unknown frame payload type"
+			" (type: 0x%02x)\n", data->ptr[0]);
+		break;
+	}
+}
+
+
+static inline struct device *ssh_rtl_get_device(struct ssh_rtl *rtl)
+{
+	return ssh_ptl_get_device(&rtl->ptl);
+}
+
+static inline bool ssh_rtl_tx_flush(struct ssh_rtl *rtl)
+{
+	return flush_work(&rtl->tx.work);
+}
+
+static inline int ssh_rtl_tx_start(struct ssh_rtl *rtl)
+{
+	int status;
+	bool sched;
+
+	status = ssh_ptl_tx_start(&rtl->ptl);
+	if (status)
+		return status;
+
+	/*
+	 * If the packet layer has been shut down and restarted without shutting
+	 * down the request layer, there may still be requests queued and not
+	 * handled.
+	 */
+	spin_lock(&rtl->queue.lock);
+	sched = !list_empty(&rtl->queue.head);
+	spin_unlock(&rtl->queue.lock);
+
+	if (sched)
+		ssh_rtl_tx_schedule(rtl);
+
+	return 0;
+}
+
+static inline int ssh_rtl_rx_start(struct ssh_rtl *rtl)
+{
+	return ssh_ptl_rx_start(&rtl->ptl);
+}
+
+static int ssh_rtl_init(struct ssh_rtl *rtl, struct serdev_device *serdev,
+			const struct ssh_rtl_ops *ops)
+{
+	struct ssh_ptl_ops ptl_ops;
+	int status;
+
+	ptl_ops.data_received = ssh_rtl_rx_data;
+
+	status = ssh_ptl_init(&rtl->ptl, serdev, &ptl_ops);
+	if (status)
+		return status;
+
+	spin_lock_init(&rtl->queue.lock);
+	INIT_LIST_HEAD(&rtl->queue.head);
+
+	spin_lock_init(&rtl->pending.lock);
+	INIT_LIST_HEAD(&rtl->pending.head);
+	atomic_set_release(&rtl->pending.count, 0);
+
+	INIT_WORK(&rtl->tx.work, ssh_rtl_tx_work_fn);
+
+	rtl->rtx_timeout.timeout = SSH_RTL_REQUEST_TIMEOUT;
+	rtl->rtx_timeout.expires = KTIME_MAX;
+	INIT_DELAYED_WORK(&rtl->rtx_timeout.reaper, ssh_rtl_timeout_reap);
+
+	rtl->ops = *ops;
+
+	return 0;
+}
+
+static void ssh_rtl_destroy(struct ssh_rtl *rtl)
+{
+	ssh_ptl_destroy(&rtl->ptl);
+}
+
+
+static void ssh_rtl_packet_release(struct ssh_packet *p)
+{
+	struct ssh_request *rqst = to_ssh_request(p, packet);
+	rqst->ops->release(rqst);
+}
+
+static const struct ssh_packet_ops ssh_rtl_packet_ops = {
+	.complete = ssh_rtl_packet_callback,
+	.release = ssh_rtl_packet_release,
+};
+
+static void ssh_request_init(struct ssh_request *rqst,
+			     enum ssam_request_flags flags,
+			     const struct ssh_request_ops *ops)
+{
+	struct ssh_packet_args packet_args;
+
+	packet_args.type = BIT(SSH_PACKET_TY_BLOCKING_BIT);
+	if (!(flags & SSAM_REQUEST_UNSEQUENCED))
+		packet_args.type |= BIT(SSH_PACKET_TY_SEQUENCED_BIT);
+
+	packet_args.priority = SSH_PACKET_PRIORITY(DATA, 0);
+	packet_args.ops = &ssh_rtl_packet_ops;
+
+	ssh_packet_init(&rqst->packet, &packet_args);
+	INIT_LIST_HEAD(&rqst->node);
+
+	rqst->state = 0;
+	if (flags & SSAM_REQUEST_HAS_RESPONSE)
+		rqst->state |= BIT(SSH_REQUEST_TY_HAS_RESPONSE_BIT);
+
+	rqst->timestamp = KTIME_MAX;
+	rqst->ops = ops;
+}
+
+
+struct ssh_flush_request {
+	struct ssh_request base;
+	struct completion completion;
+	int status;
+};
+
+static void ssh_rtl_flush_request_complete(struct ssh_request *r,
+					   const struct ssh_command *cmd,
+					   const struct ssam_span *data,
+					   int status)
+{
+	struct ssh_flush_request *rqst;
+
+	rqst = container_of(r, struct ssh_flush_request, base);
+	rqst->status = status;
+}
+
+static void ssh_rtl_flush_request_release(struct ssh_request *r)
+{
+	struct ssh_flush_request *rqst;
+
+	rqst = container_of(r, struct ssh_flush_request, base);
+	complete_all(&rqst->completion);
+}
+
+static const struct ssh_request_ops ssh_rtl_flush_request_ops = {
+	.complete = ssh_rtl_flush_request_complete,
+	.release = ssh_rtl_flush_request_release,
+};
+
+/**
+ * ssh_rtl_flush - flush the request transmission layer
+ * @rtl:     request transmission layer
+ * @timeout: timeout for the flush operation in jiffies
+ *
+ * Queue a special flush request and wait for its completion. This request
+ * will be completed after all other currently queued and pending requests
+ * have been completed. Instead of a normal data packet, this request submits
+ * a special flush packet, meaning that upon completion, also the underlying
+ * packet transmission layer has been flushed.
+ *
+ * Flushing the request layer gurarantees that all previously submitted
+ * requests have been fully completed before this call returns. Additinally,
+ * flushing blocks execution of all later submitted requests until the flush
+ * has been completed.
+ *
+ * If the caller ensures that no new requests are submitted after a call to
+ * this function, the request transmission layer is guaranteed to have no
+ * remaining requests when this call returns. The same guarantee does not hold
+ * for the packet layer, on which control packets may still be queued after
+ * this call. See the documentation of ssh_ptl_flush for more details on
+ * packet layer flushing.
+ *
+ * Return: Zero on success, -ETIMEDOUT if the flush timed out and has been
+ * canceled as a result of the timeout, or -ESHUTDOWN if the packet and/or
+ * request transmission layer has been shut down before this call. May also
+ * return -EINTR if the underlying packet transmission has been interrupted.
+ */
+static int ssh_rtl_flush(struct ssh_rtl *rtl, unsigned long timeout)
+{
+	const unsigned init_flags = SSAM_REQUEST_UNSEQUENCED;
+	struct ssh_flush_request rqst;
+	int status;
+
+	ssh_request_init(&rqst.base, init_flags, &ssh_rtl_flush_request_ops);
+	rqst.base.packet.state |= BIT(SSH_PACKET_TY_FLUSH_BIT);
+	rqst.base.packet.priority = SSH_PACKET_PRIORITY(FLUSH, 0);
+	rqst.base.state |= BIT(SSH_REQUEST_TY_FLUSH_BIT);
+
+	init_completion(&rqst.completion);
+
+	status = ssh_rtl_submit(rtl, &rqst.base);
+	if (status)
+		return status;
+
+	ssh_request_put(&rqst.base);
+
+	if (wait_for_completion_timeout(&rqst.completion, timeout))
+		return 0;
+
+	ssh_rtl_cancel(&rqst.base, true);
+	wait_for_completion(&rqst.completion);
+
+	WARN_ON(rqst.status != 0 && rqst.status != -ECANCELED
+		&& rqst.status != -ESHUTDOWN && rqst.status != -EINTR);
+
+	return rqst.status == -ECANCELED ? -ETIMEDOUT : status;
+}
+
+
+static void ssh_rtl_shutdown(struct ssh_rtl *rtl)
+{
+	struct ssh_request *r, *n;
+	LIST_HEAD(claimed);
+	int pending;
+
+	set_bit(SSH_RTL_SF_SHUTDOWN_BIT, &rtl->state);
+	smp_mb__after_atomic();
+
+	// remove requests from queue
+	spin_lock(&rtl->queue.lock);
+	list_for_each_entry_safe(r, n, &rtl->queue.head, node) {
+		set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state);
+		smp_mb__before_atomic();
+		clear_bit(SSH_REQUEST_SF_QUEUED_BIT, &r->state);
+
+		list_del(&r->node);
+		list_add_tail(&r->node, &claimed);
+	}
+	spin_unlock(&rtl->queue.lock);
+
+	/*
+	 * We have now guaranteed that the queue is empty and no more new
+	 * requests can be submitted (i.e. it will stay empty). This means that
+	 * calling ssh_rtl_tx_schedule will not schedule tx.work any more. So we
+	 * can simply call cancel_work_sync on tx.work here and when that
+	 * returns, we've locked it down. This also means that after this call,
+	 * we don't submit any more packets to the underlying packet layer, so
+	 * we can also shut that down.
+	 */
+
+	cancel_work_sync(&rtl->tx.work);
+	ssh_ptl_shutdown(&rtl->ptl);
+	cancel_delayed_work_sync(&rtl->rtx_timeout.reaper);
+
+	/*
+	 * Shutting down the packet layer should also have caneled all requests.
+	 * Thus the pending set should be empty. Attempt to handle this
+	 * gracefully anyways, even though this should be dead code.
+	 */
+
+	pending = atomic_read(&rtl->pending.count);
+	if (WARN_ON(pending)) {
+		spin_lock(&rtl->pending.lock);
+		list_for_each_entry_safe(r, n, &rtl->pending.head, node) {
+			set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state);
+			smp_mb__before_atomic();
+			clear_bit(SSH_REQUEST_SF_PENDING_BIT, &r->state);
+
+			list_del(&r->node);
+			list_add_tail(&r->node, &claimed);
+		}
+		spin_unlock(&rtl->pending.lock);
+	}
+
+	// finally cancel and complete requests
+	list_for_each_entry_safe(r, n, &claimed, node) {
+		// test_and_set because we still might compete with cancellation
+		if (!test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+			ssh_rtl_complete_with_status(r, -ESHUTDOWN);
+
+		// drop the reference we've obtained by removing it from list
+		list_del(&r->node);
+		ssh_request_put(r);
+	}
+}
+
+
+/* -- Event notifier/callbacks. --------------------------------------------- */
+/*
+ * The notifier system is based on linux/notifier.h, specifically the SRCU
+ * implementation. The difference to that is, that some bits of the notifier
+ * call return value can be tracked accross multiple calls. This is done so that
+ * handling of events can be tracked and a warning can be issued in case an
+ * event goes unhandled. The idea of that waring is that it should help discover
+ * and identify new/currently unimplemented features.
+ */
+
+struct ssam_nf_head {
+	struct srcu_struct srcu;
+	struct ssam_notifier_block __rcu *head;
+};
+
+
+int ssam_nfblk_call_chain(struct ssam_nf_head *nh, struct ssam_event *event)
+{
+	struct ssam_notifier_block *nb, *next_nb;
+	int ret = 0, idx;
+
+	idx = srcu_read_lock(&nh->srcu);
+
+	nb = rcu_dereference_raw(nh->head);
+	while (nb) {
+		next_nb = rcu_dereference_raw(nb->next);
+
+		ret = (ret & SSAM_NOTIF_STATE_MASK) | nb->fn(nb, event);
+		if (ret & SSAM_NOTIF_STOP)
+			break;
+
+		nb = next_nb;
+	}
+
+	srcu_read_unlock(&nh->srcu, idx);
+	return ret;
+}
+
+/*
+ * Note: This function must be synchronized by the caller with respect to other
+ * insert and/or remove calls.
+ */
+int __ssam_nfblk_insert(struct ssam_nf_head *nh, struct ssam_notifier_block *nb)
+{
+	struct ssam_notifier_block **link = &nh->head;
+
+	while ((*link) != NULL) {
+		if (unlikely((*link) == nb)) {
+			WARN(1, "double register detected");
+			return -EINVAL;
+		}
+
+		if (nb->priority > (*link)->priority)
+			break;
+
+		link = &((*link)->next);
+	}
+
+	nb->next = *link;
+	rcu_assign_pointer(*link, nb);
+
+	return 0;
+}
+
+/*
+ * Note: This function must be synchronized by the caller with respect to other
+ * insert and/or remove calls. On success, the caller _must_ ensure SRCU
+ * synchronization by calling `synchronize_srcu(&nh->srcu)` after leaving the
+ * critical section, to ensure that the removed notifier block is not in use any
+ * more.
+ */
+int __ssam_nfblk_remove(struct ssam_nf_head *nh, struct ssam_notifier_block *nb)
+{
+	struct ssam_notifier_block **link = &nh->head;
+
+	while ((*link) != NULL) {
+		if ((*link) == nb) {
+			rcu_assign_pointer(*link, nb->next);
+			return 0;
+		}
+
+		link = &((*link)->next);
+	}
+
+	return -ENOENT;
+}
+
+static int ssam_nf_head_init(struct ssam_nf_head *nh)
+{
+	int status;
+
+	status = init_srcu_struct(&nh->srcu);
+	if (status)
+		return status;
+
+	nh->head = NULL;
+	return 0;
+}
+
+static void ssam_nf_head_destroy(struct ssam_nf_head *nh)
+{
+	cleanup_srcu_struct(&nh->srcu);
+}
+
+
+/* -- Event/notification registry. ------------------------------------------ */
+
+struct ssam_nf_refcount_key {
+	struct ssam_event_registry reg;
+	struct ssam_event_id id;
+};
+
+struct ssam_nf_refcount_entry {
+	struct rb_node node;
+	struct ssam_nf_refcount_key key;
+	int refcount;
+};
+
+struct ssam_nf {
+	struct mutex lock;
+	struct rb_root refcount;
+	struct ssam_nf_head head[SSH_NUM_EVENTS];
+};
+
+
+static int ssam_nf_refcount_inc(struct ssam_nf *nf,
+				struct ssam_event_registry reg,
+				struct ssam_event_id id)
+{
+	struct ssam_nf_refcount_entry *entry;
+	struct ssam_nf_refcount_key key;
+	struct rb_node **link = &nf->refcount.rb_node;
+	struct rb_node *parent = NULL;
+	int cmp;
+
+	key.reg = reg;
+	key.id = id;
+
+	while (*link) {
+		entry = rb_entry(*link, struct ssam_nf_refcount_entry, node);
+		parent = *link;
+
+		cmp = memcmp(&key, &entry->key, sizeof(key));
+		if (cmp < 0) {
+			link = &(*link)->rb_left;
+		} else if (cmp > 0) {
+			link = &(*link)->rb_right;
+		} else if (entry->refcount < INT_MAX) {
+			return ++entry->refcount;
+		} else {
+			return -ENOSPC;
+		}
+	}
+
+	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+	if (!entry)
+		return -ENOMEM;
+
+	entry->key = key;
+	entry->refcount = 1;
+
+	rb_link_node(&entry->node, parent, link);
+	rb_insert_color(&entry->node, &nf->refcount);
+
+	return entry->refcount;
+}
+
+static int ssam_nf_refcount_dec(struct ssam_nf *nf,
+				struct ssam_event_registry reg,
+				struct ssam_event_id id)
+{
+	struct ssam_nf_refcount_entry *entry;
+	struct ssam_nf_refcount_key key;
+	struct rb_node *node = nf->refcount.rb_node;
+	int cmp, rc;
+
+	key.reg = reg;
+	key.id = id;
+
+	while (node) {
+		entry = rb_entry(node, struct ssam_nf_refcount_entry, node);
+
+		cmp = memcmp(&key, &entry->key, sizeof(key));
+		if (cmp < 0) {
+			node = node->rb_left;
+		} else if (cmp > 0) {
+			node = node->rb_right;
+		} else {
+			rc = --entry->refcount;
+
+			if (rc == 0) {
+				rb_erase(&entry->node, &nf->refcount);
+				kfree(entry);
+			}
+
+			return rc;
+		}
+	}
+
+	return -ENOENT;
+}
+
+static bool ssam_nf_refcount_empty(struct ssam_nf *nf)
+{
+	return RB_EMPTY_ROOT(&nf->refcount);
+}
+
+static void ssam_nf_call(struct ssam_nf *nf, struct device *dev, u16 rqid,
+			 struct ssam_event *event)
+{
+	struct ssam_nf_head *nf_head;
+	int status, nf_ret;
+
+	if (!ssh_rqid_is_event(rqid)) {
+		dev_warn(dev, "event: unsupported rqid: 0x%04x\n", rqid);
+		return;
+	}
+
+	nf_head = &nf->head[ssh_rqid_to_event(rqid)];
+	nf_ret = ssam_nfblk_call_chain(nf_head, event);
+	status = ssam_notifier_to_errno(nf_ret);
+
+	if (status < 0) {
+		dev_err(dev, "event: error handling event: %d "
+			"(tc: 0x%02x, cid: 0x%02x, iid: 0x%02x, chn: 0x%02x)\n",
+			status, event->target_category, event->command_id,
+			event->instance_id, event->channel);
+	}
+
+	if (!(nf_ret & SSAM_NOTIF_HANDLED)) {
+		dev_warn(dev, "event: unhandled event (rqid: 0x%02x, "
+			 "tc: 0x%02x, cid: 0x%02x, iid: 0x%02x, chn: 0x%02x)\n",
+			 rqid, event->target_category, event->command_id,
+			 event->instance_id, event->channel);
+	}
+}
+
+static int ssam_nf_init(struct ssam_nf *nf)
+{
+	int i, status;
+
+	for (i = 0; i < SSH_NUM_EVENTS; i++) {
+		status = ssam_nf_head_init(&nf->head[i]);
+		if (status)
+			break;
+	}
+
+	if (status) {
+		for (i = i - 1; i >= 0; i--)
+			ssam_nf_head_destroy(&nf->head[i]);
+
+		return status;
+	}
+
+	mutex_init(&nf->lock);
+	return 0;
+}
+
+static void ssam_nf_destroy(struct ssam_nf *nf)
+{
+	int i;
+
+	for (i = 0; i < SSH_NUM_EVENTS; i++)
+		ssam_nf_head_destroy(&nf->head[i]);
+
+	mutex_destroy(&nf->lock);
+}
+
+
+/* -- Event/async request completion system. -------------------------------- */
+
+#define SSAM_CPLT_WQ_NAME	"ssam_cpltq"
+
+
+struct ssam_cplt;
+struct ssam_event_item;
+
+struct ssam_event_item_ops {
+	void (*free)(struct ssam_event_item *);
+};
+
+struct ssam_event_item {
+	struct list_head node;
+	u16 rqid;
+
+	struct ssam_event_item_ops ops;
+	struct ssam_event event;	// must be last
+};
+
+struct ssam_event_queue {
+	struct ssam_cplt *cplt;
+
+	spinlock_t lock;
+	struct list_head head;
+	struct work_struct work;
+};
+
+struct ssam_event_channel {
+	struct ssam_event_queue queue[SSH_NUM_EVENTS];
+};
+
+struct ssam_cplt {
+	struct device *dev;
+	struct workqueue_struct *wq;
+
+	struct {
+		struct ssam_event_channel channel[SSH_NUM_CHANNELS];
+		struct ssam_nf notif;
+	} event;
+};
+
+
+/**
+ * Maximum payload length for cached `ssam_event_item`s.
+ *
+ * This length has been chosen to be accomodate standard touchpad and keyboard
+ * input events. Events with larger payloads will be allocated separately.
+ */
+#define SSAM_EVENT_ITEM_CACHE_PAYLOAD_LEN	32
+
+static struct kmem_cache *ssam_event_item_cache;
+
+static int ssam_event_item_cache_init(void)
+{
+	const unsigned int size = sizeof(struct ssam_event_item)
+				  + SSAM_EVENT_ITEM_CACHE_PAYLOAD_LEN;
+	const unsigned int align = __alignof__(struct ssam_event_item);
+	struct kmem_cache *cache;
+
+	cache = kmem_cache_create("ssam_event_item", size, align, 0, NULL);
+	if (!cache)
+		return -ENOMEM;
+
+	ssam_event_item_cache = cache;
+	return 0;
+}
+
+static void ssam_event_item_cache_destroy(void)
+{
+	kmem_cache_destroy(ssam_event_item_cache);
+	ssam_event_item_cache = NULL;
+}
+
+static void __ssam_event_item_free_cached(struct ssam_event_item *item)
+{
+	kmem_cache_free(ssam_event_item_cache, item);
+}
+
+static void __ssam_event_item_free_generic(struct ssam_event_item *item)
+{
+	kfree(item);
+}
+
+static inline void ssam_event_item_free(struct ssam_event_item *item)
+{
+	trace_ssam_event_item_free(item);
+	item->ops.free(item);
+}
+
+static struct ssam_event_item *ssam_event_item_alloc(size_t len, gfp_t flags)
+{
+	struct ssam_event_item *item;
+
+	if (len <= SSAM_EVENT_ITEM_CACHE_PAYLOAD_LEN) {
+		item = kmem_cache_alloc(ssam_event_item_cache, GFP_KERNEL);
+		if (!item)
+			return NULL;
+
+		item->ops.free = __ssam_event_item_free_cached;
+	} else {
+		const size_t n = sizeof(struct ssam_event_item) + len;
+		item = kzalloc(n, GFP_KERNEL);
+		if (!item)
+			return NULL;
+
+		item->ops.free = __ssam_event_item_free_generic;
+	}
+
+	item->event.length = len;
+
+	trace_ssam_event_item_alloc(item, len);
+	return item;
+}
+
+
+static void ssam_event_queue_push(struct ssam_event_queue *q,
+				  struct ssam_event_item *item)
+{
+	spin_lock(&q->lock);
+	list_add_tail(&item->node, &q->head);
+	spin_unlock(&q->lock);
+}
+
+static struct ssam_event_item *ssam_event_queue_pop(struct ssam_event_queue *q)
+{
+	struct ssam_event_item *item;
+
+	spin_lock(&q->lock);
+	item = list_first_entry_or_null(&q->head, struct ssam_event_item, node);
+	if (item)
+		list_del(&item->node);
+	spin_unlock(&q->lock);
+
+	return item;
+}
+
+static bool ssam_event_queue_is_empty(struct ssam_event_queue *q)
+{
+	bool empty;
+
+	spin_lock(&q->lock);
+	empty = list_empty(&q->head);
+	spin_unlock(&q->lock);
+
+	return empty;
+}
+
+static struct ssam_event_queue *ssam_cplt_get_event_queue(
+		struct ssam_cplt *cplt, u8 channel, u16 rqid)
+{
+	u16 event = ssh_rqid_to_event(rqid);
+	u16 chidx = ssh_channel_to_index(channel);
+
+	if (!ssh_rqid_is_event(rqid)) {
+		dev_err(cplt->dev, "event: unsupported rqid: 0x%04x\n", rqid);
+		return NULL;
+	}
+
+	if (!ssh_channel_is_valid(channel)) {
+		dev_warn(cplt->dev, "event: unsupported channel: %u\n",
+			 channel);
+		chidx = 0;
+	}
+
+	return &cplt->event.channel[chidx].queue[event];
+}
+
+static inline bool ssam_cplt_submit(struct ssam_cplt *cplt,
+				    struct work_struct *work)
+{
+	return queue_work(cplt->wq, work);
+}
+
+static int ssam_cplt_submit_event(struct ssam_cplt *cplt,
+				  struct ssam_event_item *item)
+{
+	struct ssam_event_queue *evq;
+
+	evq = ssam_cplt_get_event_queue(cplt, item->event.channel, item->rqid);
+	if (!evq)
+		return -EINVAL;
+
+	ssam_event_queue_push(evq, item);
+	ssam_cplt_submit(cplt, &evq->work);
+	return 0;
+}
+
+static void ssam_cplt_flush(struct ssam_cplt *cplt)
+{
+	flush_workqueue(cplt->wq);
+}
+
+static void ssam_event_queue_work_fn(struct work_struct *work)
+{
+	struct ssam_event_queue *queue;
+	struct ssam_event_item *item;
+	struct ssam_nf *nf;
+	struct device *dev;
+	int i;
+
+	queue = container_of(work, struct ssam_event_queue, work);
+	nf = &queue->cplt->event.notif;
+	dev = queue->cplt->dev;
+
+	for (i = 0; i < 10; i++) {
+		item = ssam_event_queue_pop(queue);
+		if (item == NULL)
+			return;
+
+		ssam_nf_call(nf, dev, item->rqid, &item->event);
+		ssam_event_item_free(item);
+	}
+
+	if (!ssam_event_queue_is_empty(queue))
+		ssam_cplt_submit(queue->cplt, &queue->work);
+}
+
+static void ssam_event_queue_init(struct ssam_cplt *cplt,
+				  struct ssam_event_queue *evq)
+{
+	evq->cplt = cplt;
+	spin_lock_init(&evq->lock);
+	INIT_LIST_HEAD(&evq->head);
+	INIT_WORK(&evq->work, ssam_event_queue_work_fn);
+}
+
+static int ssam_cplt_init(struct ssam_cplt *cplt, struct device *dev)
+{
+	struct ssam_event_channel *channel;
+	int status, c, i;
+
+	cplt->dev = dev;
+
+	cplt->wq = create_workqueue(SSAM_CPLT_WQ_NAME);
+	if (!cplt->wq)
+		return -ENOMEM;
+
+	for (c = 0; c < ARRAY_SIZE(cplt->event.channel); c++) {
+		channel = &cplt->event.channel[c];
+
+		for (i = 0; i < ARRAY_SIZE(channel->queue); i++)
+			ssam_event_queue_init(cplt, &channel->queue[i]);
+	}
+
+	status = ssam_nf_init(&cplt->event.notif);
+	if (status)
+		destroy_workqueue(cplt->wq);
+
+	return status;
+}
+
+static void ssam_cplt_destroy(struct ssam_cplt *cplt)
+{
+	/*
+	 * Note: destroy_workqueue ensures that all currently queued work will
+	 * be fully completed and the workqueue drained. This means that this
+	 * call will inherently also free any queued ssam_event_items, thus we
+	 * don't have to take care of that here explicitly.
+	 */
+	destroy_workqueue(cplt->wq);
+	ssam_nf_destroy(&cplt->event.notif);
+}
+
+
+/* -- Main SSAM device structures. ------------------------------------------ */
+
+enum ssam_controller_state {
+	SSAM_CONTROLLER_UNINITIALIZED,
+	SSAM_CONTROLLER_INITIALIZED,
+	SSAM_CONTROLLER_STARTED,
+	SSAM_CONTROLLER_STOPPED,
+	SSAM_CONTROLLER_SUSPENDED,
+};
+
+struct ssam_device_caps {
+	u32 notif_display:1;
+	u32 notif_d0exit:1;
+};
+
+struct ssam_controller {
+	enum ssam_controller_state state;
+
+	struct ssh_rtl rtl;
+	struct ssam_cplt cplt;
+
+	struct {
+		struct ssh_seq_counter seq;
+		struct ssh_rqid_counter rqid;
+	} counter;
+
+	struct {
+		int num;
+		bool wakeup_enabled;
+	} irq;
+
+	struct ssam_device_caps caps;
+};
+
+
+#define ssam_dbg(ctrl, fmt, ...)  rtl_dbg(&(ctrl)->rtl, fmt, ##__VA_ARGS__)
+#define ssam_info(ctrl, fmt, ...) rtl_info(&(ctrl)->rtl, fmt, ##__VA_ARGS__)
+#define ssam_warn(ctrl, fmt, ...) rtl_warn(&(ctrl)->rtl, fmt, ##__VA_ARGS__)
+#define ssam_err(ctrl, fmt, ...)  rtl_err(&(ctrl)->rtl, fmt, ##__VA_ARGS__)
+
+#define to_ssam_controller(ptr, member) \
+	container_of(ptr, struct ssam_controller, member)
+
+struct device *ssam_controller_device(struct ssam_controller *c)
+{
+	return ssh_rtl_get_device(&c->rtl);
+}
+EXPORT_SYMBOL_GPL(ssam_controller_device);
+
+
+static void ssam_handle_event(struct ssh_rtl *rtl,
+			      const struct ssh_command *cmd,
+			      const struct ssam_span *data)
+{
+	struct ssam_controller *ctrl = to_ssam_controller(rtl, rtl);
+	struct ssam_event_item *item;
+
+	item = ssam_event_item_alloc(data->len, GFP_KERNEL);
+	if (!item)
+		return;
+
+	item->rqid = get_unaligned_le16(&cmd->rqid);
+	item->event.target_category = cmd->tc;
+	item->event.command_id = cmd->cid;
+	item->event.instance_id = cmd->iid;
+	item->event.channel = cmd->chn_in;
+	memcpy(&item->event.data[0], data->ptr, data->len);
+
+	ssam_cplt_submit_event(&ctrl->cplt, item);
+}
+
+static const struct ssh_rtl_ops ssam_rtl_ops = {
+	.handle_event = ssam_handle_event,
+};
+
+
+static bool ssam_notifier_empty(struct ssam_controller *ctrl);
+static void ssam_notifier_unregister_all(struct ssam_controller *ctrl);
+
+
+#define SSAM_SSH_DSM_REVISION	0
+#define SSAM_SSH_DSM_NOTIF_D0	8
+static const guid_t SSAM_SSH_DSM_UUID = GUID_INIT(0xd5e383e1, 0xd892, 0x4a76,
+		0x89, 0xfc, 0xf6, 0xaa, 0xae, 0x7e, 0xd5, 0xb5);
+
+static int ssam_device_caps_load_from_acpi(acpi_handle handle,
+					   struct ssam_device_caps *caps)
+{
+	union acpi_object *obj;
+	u64 funcs = 0;
+	int i;
+
+	// set defaults
+	caps->notif_display = true;
+	caps->notif_d0exit = false;
+
+	if (!acpi_has_method(handle, "_DSM"))
+		return 0;
+
+	// get function availability bitfield
+	obj = acpi_evaluate_dsm_typed(handle, &SSAM_SSH_DSM_UUID, 0, 0, NULL,
+			ACPI_TYPE_BUFFER);
+	if (!obj)
+		return -EFAULT;
+
+	for (i = 0; i < obj->buffer.length && i < 8; i++)
+		funcs |= (((u64)obj->buffer.pointer[i]) << (i * 8));
+
+	ACPI_FREE(obj);
+
+	// D0 exit/entry notification
+	if (funcs & BIT(SSAM_SSH_DSM_NOTIF_D0)) {
+		obj = acpi_evaluate_dsm_typed(handle, &SSAM_SSH_DSM_UUID,
+				SSAM_SSH_DSM_REVISION, SSAM_SSH_DSM_NOTIF_D0,
+				NULL, ACPI_TYPE_INTEGER);
+		if (!obj)
+			return -EFAULT;
+
+		caps->notif_d0exit = !!obj->integer.value;
+		ACPI_FREE(obj);
+	}
+
+	return 0;
+}
+
+static int ssam_controller_init(struct ssam_controller *ctrl,
+				struct serdev_device *serdev)
+{
+	acpi_handle handle = ACPI_HANDLE(&serdev->dev);
+	int status;
+
+	if (smp_load_acquire(&ctrl->state) != SSAM_CONTROLLER_UNINITIALIZED) {
+		dev_err(&serdev->dev, "embedded controller already initialized\n");
+		return -EBUSY;
+	}
+
+	status = ssam_device_caps_load_from_acpi(handle, &ctrl->caps);
+	if (status)
+		return status;
+
+	dev_dbg(&serdev->dev, "device capabilities:\n");
+	dev_dbg(&serdev->dev, "  notif_display: %u\n", ctrl->caps.notif_display);
+	dev_dbg(&serdev->dev, "  notif_d0exit:  %u\n", ctrl->caps.notif_d0exit);
+
+	ssh_seq_reset(&ctrl->counter.seq);
+	ssh_rqid_reset(&ctrl->counter.rqid);
+
+	// initialize event/request completion system
+	status = ssam_cplt_init(&ctrl->cplt, &serdev->dev);
+	if (status)
+		return status;
+
+	// initialize request and packet transmission layers
+	status = ssh_rtl_init(&ctrl->rtl, serdev, &ssam_rtl_ops);
+	if (status) {
+		ssam_cplt_destroy(&ctrl->cplt);
+		return status;
+	}
+
+	// update state
+	smp_store_release(&ctrl->state, SSAM_CONTROLLER_INITIALIZED);
+	return 0;
+}
+
+static int ssam_controller_start(struct ssam_controller *ctrl)
+{
+	int status;
+
+	if (smp_load_acquire(&ctrl->state) != SSAM_CONTROLLER_INITIALIZED)
+		return -EINVAL;
+
+	status = ssh_rtl_tx_start(&ctrl->rtl);
+	if (status)
+		return status;
+
+	status = ssh_rtl_rx_start(&ctrl->rtl);
+	if (status) {
+		ssh_rtl_tx_flush(&ctrl->rtl);
+		return status;
+	}
+
+	smp_store_release(&ctrl->state, SSAM_CONTROLLER_STARTED);
+	return 0;
+}
+
+static void ssam_controller_shutdown(struct ssam_controller *ctrl)
+{
+	enum ssam_controller_state s = smp_load_acquire(&ctrl->state);
+	int status;
+
+	if (s == SSAM_CONTROLLER_UNINITIALIZED || s == SSAM_CONTROLLER_STOPPED)
+		return;
+
+	// try to flush pending events and requests while everything still works
+	status = ssh_rtl_flush(&ctrl->rtl, msecs_to_jiffies(5000));
+	if (status) {
+		ssam_err(ctrl, "failed to flush request transmission layer: %d\n",
+			 status);
+	}
+
+	// try to flush out all currently completing requests and events
+	ssam_cplt_flush(&ctrl->cplt);
+
+	/*
+	 * We expect all notifiers to have been removed by the respective client
+	 * driver that set them up at this point. If this warning occurs, some
+	 * client driver has not done that...
+	 */
+	WARN_ON(!ssam_notifier_empty(ctrl));
+
+	/*
+	 * Nevertheless, we should still take care of drivers that don't behave
+	 * well. Thus disable all enabled events, unregister all notifiers.
+	 */
+	ssam_notifier_unregister_all(ctrl);
+
+	// cancel rem. requests, ensure no new ones can be queued, stop threads
+	ssh_rtl_tx_flush(&ctrl->rtl);
+	ssh_rtl_shutdown(&ctrl->rtl);
+
+	smp_store_release(&ctrl->state, SSAM_CONTROLLER_STOPPED);
+}
+
+static void ssam_controller_destroy(struct ssam_controller *ctrl)
+{
+	if (smp_load_acquire(&ctrl->state) == SSAM_CONTROLLER_UNINITIALIZED)
+		return;
+
+	/*
+	 * Note: New events could still have been received after the previous
+	 * flush in ssam_controller_shutdown, before the request transport layer
+	 * has been shut down. At this point, after the shutdown, we can be sure
+	 * that no new events will be queued. The call to ssam_cplt_destroy will
+	 * ensure that those remaining are being completed and freed.
+	 */
+
+	// actually free resources
+	ssam_cplt_destroy(&ctrl->cplt);
+	ssh_rtl_destroy(&ctrl->rtl);
+
+	smp_store_release(&ctrl->state, SSAM_CONTROLLER_UNINITIALIZED);
+}
+
+static int ssam_controller_suspend(struct ssam_controller *ctrl)
+{
+	if (smp_load_acquire(&ctrl->state) != SSAM_CONTROLLER_STARTED)
+		return -EINVAL;
+
+	ssam_dbg(ctrl, "pm: suspending controller\n");
+	smp_store_release(&ctrl->state, SSAM_CONTROLLER_SUSPENDED);
+	return 0;
+}
+
+static int ssam_controller_resume(struct ssam_controller *ctrl)
+{
+	if (smp_load_acquire(&ctrl->state) != SSAM_CONTROLLER_SUSPENDED)
+		return -EINVAL;
+
+	ssam_dbg(ctrl, "pm: resuming controller\n");
+	smp_store_release(&ctrl->state, SSAM_CONTROLLER_STARTED);
+	return 0;
+}
+
+
+static inline
+int ssam_controller_receive_buf(struct ssam_controller *ctrl,
+				const unsigned char *buf, size_t n)
+{
+	return ssh_ptl_rx_rcvbuf(&ctrl->rtl.ptl, buf, n);
+}
+
+static inline void ssam_controller_write_wakeup(struct ssam_controller *ctrl)
+{
+	ssh_ptl_tx_wakeup(&ctrl->rtl.ptl, true);
+}
+
+
+/* -- Top-level request interface ------------------------------------------- */
+
+ssize_t ssam_request_write_data(struct ssam_span *buf,
+				struct ssam_controller *ctrl,
+				struct ssam_request *spec)
+{
+	struct msgbuf msgb;
+	u16 rqid;
+	u8 seq;
+
+	if (spec->length > SSH_COMMAND_MAX_PAYLOAD_SIZE)
+		return -EINVAL;
+
+	msgb_init(&msgb, buf->ptr, buf->len);
+	seq = ssh_seq_next(&ctrl->counter.seq);
+	rqid = ssh_rqid_next(&ctrl->counter.rqid);
+	msgb_push_cmd(&msgb, seq, rqid, spec);
+
+	return msgb_bytes_used(&msgb);
+}
+EXPORT_SYMBOL_GPL(ssam_request_write_data);
+
+
+static void ssam_request_sync_complete(struct ssh_request *rqst,
+				       const struct ssh_command *cmd,
+				       const struct ssam_span *data, int status)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+	struct ssam_request_sync *r;
+
+	r = container_of(rqst, struct ssam_request_sync, base);
+	r->status = status;
+
+        if (r->resp)
+	        r->resp->length = 0;
+
+	if (status) {
+		rtl_dbg_cond(rtl, "rsp: request failed: %d\n", status);
+		return;
+	}
+
+	if (!data)	// handle requests without a response
+		return;
+
+	if (!r->resp || !r->resp->pointer) {
+                if (data->len) {
+		        rtl_warn(rtl, "rsp: no response buffer provided, "
+                                 "dropping data\n");
+                }
+                return;
+        }
+
+	if (data->len > r->resp->capacity) {
+		rtl_err(rtl, "rsp: response buffer too small, "
+			"capacity: %zu bytes, got: %zu bytes\n",
+			r->resp->capacity, data->len);
+		r->status = -ENOSPC;
+		return;
+	}
+
+	r->resp->length = data->len;
+	memcpy(r->resp->pointer, data->ptr, data->len);
+}
+
+static void ssam_request_sync_release(struct ssh_request *rqst)
+{
+	complete_all(&container_of(rqst, struct ssam_request_sync, base)->comp);
+}
+
+static const struct ssh_request_ops ssam_request_sync_ops = {
+	.release = ssam_request_sync_release,
+	.complete = ssam_request_sync_complete,
+};
+
+
+int ssam_request_sync_alloc(size_t payload_len, gfp_t flags,
+			    struct ssam_request_sync **rqst,
+			    struct ssam_span *buffer)
+{
+	size_t msglen = SSH_COMMAND_MESSAGE_LENGTH(payload_len);
+
+	*rqst = kzalloc(sizeof(struct ssam_request_sync) + msglen, flags);
+	if (!*rqst)
+		return -ENOMEM;
+
+	buffer->ptr = (u8 *)(*rqst + 1);
+	buffer->len = msglen;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ssam_request_sync_alloc);
+
+void ssam_request_sync_init(struct ssam_request_sync *rqst,
+			    enum ssam_request_flags flags)
+{
+	ssh_request_init(&rqst->base, flags, &ssam_request_sync_ops);
+	init_completion(&rqst->comp);
+	rqst->resp = NULL;
+	rqst->status = 0;
+}
+EXPORT_SYMBOL_GPL(ssam_request_sync_init);
+
+int ssam_request_sync_submit(struct ssam_controller *ctrl,
+			     struct ssam_request_sync *rqst)
+{
+	enum ssam_controller_state state = smp_load_acquire(&ctrl->state);
+	int status;
+
+	if (state == SSAM_CONTROLLER_SUSPENDED) {
+		ssam_warn(ctrl, "rqst: embedded controller is suspended\n");
+		ssh_request_put(&rqst->base);
+		return -EPERM;
+	}
+
+	if (state != SSAM_CONTROLLER_STARTED) {
+		ssam_warn(ctrl, "rqst: embedded controller is uninitialized\n");
+		ssh_request_put(&rqst->base);
+		return -ENXIO;
+	}
+
+	status = ssh_rtl_submit(&ctrl->rtl, &rqst->base);
+	ssh_request_put(&rqst->base);
+
+	return status;
+}
+EXPORT_SYMBOL_GPL(ssam_request_sync_submit);
+
+int ssam_request_sync(struct ssam_controller *ctrl, struct ssam_request *spec,
+		      struct ssam_response *rsp)
+{
+	struct ssam_request_sync *rqst;
+	struct ssam_span buf;
+	size_t len;
+	int status;
+
+	// prevent overflow, allows us to skip checks later on
+	if (spec->length > SSH_COMMAND_MAX_PAYLOAD_SIZE) {
+		ssam_err(ctrl, "rqst: request payload too large\n");
+		return -EINVAL;
+	}
+
+	status = ssam_request_sync_alloc(spec->length, GFP_KERNEL, &rqst, &buf);
+	if (status)
+		return status;
+
+	ssam_request_sync_init(rqst, spec->flags);
+	ssam_request_sync_set_resp(rqst, rsp);
+
+	len = ssam_request_write_data(&buf, ctrl, spec);
+	ssam_request_sync_set_data(rqst, buf.ptr, len);
+
+	status = ssam_request_sync_submit(ctrl, rqst);
+	if (!status)
+		status = ssam_request_sync_wait(rqst);
+
+	kfree(rqst);
+	return status;
+}
+EXPORT_SYMBOL_GPL(ssam_request_sync);
+
+int ssam_request_sync_with_buffer(struct ssam_controller *ctrl,
+				  struct ssam_request *spec,
+				  struct ssam_response *rsp,
+				  struct ssam_span *buf)
+{
+	struct ssam_request_sync rqst;
+	size_t len;
+	int status;
+
+	// prevent overflow, allows us to skip checks later on
+	if (spec->length > SSH_COMMAND_MAX_PAYLOAD_SIZE) {
+		ssam_err(ctrl, "rqst: request payload too large\n");
+		return -EINVAL;
+	}
+
+	ssam_request_sync_init(&rqst, spec->flags);
+	ssam_request_sync_set_resp(&rqst, rsp);
+
+	len = ssam_request_write_data(buf, ctrl, spec);
+	ssam_request_sync_set_data(&rqst, buf->ptr, len);
+
+	status = ssam_request_sync_submit(ctrl, &rqst);
+	if (!status)
+		status = ssam_request_sync_wait(&rqst);
+
+	return status;
+}
+EXPORT_SYMBOL_GPL(ssam_request_sync_with_buffer);
+
+
+/* -- Internal SAM requests. ------------------------------------------------ */
+
+static SSAM_DEFINE_SYNC_REQUEST_R(ssam_ssh_get_firmware_version, __le32, {
+	.target_category = SSAM_SSH_TC_SAM,
+	.command_id      = 0x13,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static SSAM_DEFINE_SYNC_REQUEST_R(ssam_ssh_notif_display_off, u8, {
+	.target_category = SSAM_SSH_TC_SAM,
+	.command_id      = 0x15,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static SSAM_DEFINE_SYNC_REQUEST_R(ssam_ssh_notif_display_on, u8, {
+	.target_category = SSAM_SSH_TC_SAM,
+	.command_id      = 0x16,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static SSAM_DEFINE_SYNC_REQUEST_R(ssam_ssh_notif_d0_exit, u8, {
+	.target_category = SSAM_SSH_TC_SAM,
+	.command_id      = 0x33,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static SSAM_DEFINE_SYNC_REQUEST_R(ssam_ssh_notif_d0_entry, u8, {
+	.target_category = SSAM_SSH_TC_SAM,
+	.command_id      = 0x34,
+	.instance_id     = 0x00,
+	.channel         = 0x01,
+});
+
+static int ssam_ssh_event_enable(struct ssam_controller *ctrl,
+				 struct ssam_event_registry reg,
+				 struct ssam_event_id id, u8 flags)
+{
+	struct ssh_notification_params params;
+	struct ssam_request rqst;
+	struct ssam_response result;
+	int status;
+
+	u16 rqid = ssh_tc_to_rqid(id.target_category);
+	u8 buf[1] = { 0x00 };
+
+	// only allow RQIDs that lie within event spectrum
+	if (!ssh_rqid_is_event(rqid))
+		return -EINVAL;
+
+	params.target_category = id.target_category;
+	params.instance_id = id.instance;
+	params.flags = flags;
+	put_unaligned_le16(rqid, &params.request_id);
+
+	rqst.target_category = reg.target_category;
+	rqst.command_id = reg.cid_enable;
+	rqst.instance_id = 0x00;
+	rqst.channel = reg.channel;
+	rqst.flags = SSAM_REQUEST_HAS_RESPONSE;
+	rqst.length = sizeof(params);
+	rqst.payload = (u8 *)&params;
+
+	result.capacity = ARRAY_SIZE(buf);
+	result.length = 0;
+	result.pointer = buf;
+
+	status = ssam_request_sync_onstack(ctrl, &rqst, &result, sizeof(params));
+	if (status) {
+		ssam_err(ctrl, "failed to enable event source "
+			 "(tc: 0x%02x, iid: 0x%02x, reg: 0x%02x)\n",
+			 id.target_category, id.instance, reg.target_category);
+	}
+
+	if (buf[0] != 0x00) {
+		ssam_warn(ctrl, "unexpected result while enabling event source: "
+			  "0x%02x (tc: 0x%02x, iid: 0x%02x, reg: 0x%02x)\n",
+			  buf[0], id.target_category, id.instance,
+			  reg.target_category);
+	}
+
+	return status;
+
+}
+
+static int ssam_ssh_event_disable(struct ssam_controller *ctrl,
+				  struct ssam_event_registry reg,
+				  struct ssam_event_id id, u8 flags)
+{
+	struct ssh_notification_params params;
+	struct ssam_request rqst;
+	struct ssam_response result;
+	int status;
+
+	u16 rqid = ssh_tc_to_rqid(id.target_category);
+	u8 buf[1] = { 0x00 };
+
+	// only allow RQIDs that lie within event spectrum
+	if (!ssh_rqid_is_event(rqid))
+		return -EINVAL;
+
+	params.target_category = id.target_category;
+	params.instance_id = id.instance;
+	params.flags = flags;
+	put_unaligned_le16(rqid, &params.request_id);
+
+	rqst.target_category = reg.target_category;
+	rqst.command_id = reg.cid_disable;
+	rqst.instance_id = 0x00;
+	rqst.channel = reg.channel;
+	rqst.flags = SSAM_REQUEST_HAS_RESPONSE;
+	rqst.length = sizeof(params);
+	rqst.payload = (u8 *)&params;
+
+	result.capacity = ARRAY_SIZE(buf);
+	result.length = 0;
+	result.pointer = buf;
+
+	status = ssam_request_sync_onstack(ctrl, &rqst, &result, sizeof(params));
+	if (status) {
+		ssam_err(ctrl, "failed to disable event source "
+			 "(tc: 0x%02x, iid: 0x%02x, reg: 0x%02x)\n",
+			 id.target_category, id.instance, reg.target_category);
+	}
+
+	if (buf[0] != 0x00) {
+		ssam_warn(ctrl, "unexpected result while disabling event source: "
+			  "0x%02x (tc: 0x%02x, iid: 0x%02x, reg: 0x%02x)\n",
+			  buf[0], id.target_category, id.instance,
+			  reg.target_category);
+	}
+
+	return status;
+}
+
+
+/* -- Wrappers for internal SAM requests. ----------------------------------- */
+
+static int ssam_log_firmware_version(struct ssam_controller *ctrl)
+{
+	__le32 __version;
+	u32 version, a, b, c;
+	int status;
+
+	status = ssam_ssh_get_firmware_version(ctrl, &__version);
+	if (status)
+		return status;
+
+	version = le32_to_cpu(__version);
+	a = (version >> 24) & 0xff;
+	b = ((version >> 8) & 0xffff);
+	c = version & 0xff;
+
+	ssam_info(ctrl, "SAM controller version: %u.%u.%u\n", a, b, c);
+	return 0;
+}
+
+static int ssam_ctrl_notif_display_off(struct ssam_controller *ctrl)
+{
+	int status;
+	u8 response;
+
+	if (!ctrl->caps.notif_display)
+		return 0;
+
+	ssam_dbg(ctrl, "pm: notifying display off\n");
+
+	status = ssam_ssh_notif_display_off(ctrl, &response);
+	if (status)
+		return status;
+
+	if (response != 0) {
+		ssam_err(ctrl, "unexpected response from display-off notification: "
+			 "0x%02x\n", response);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int ssam_ctrl_notif_display_on(struct ssam_controller *ctrl)
+{
+	int status;
+	u8 response;
+
+	if (!ctrl->caps.notif_display)
+		return 0;
+
+	ssam_dbg(ctrl, "pm: notifying display on\n");
+
+	status = ssam_ssh_notif_display_on(ctrl, &response);
+	if (status)
+		return status;
+
+	if (response != 0) {
+		ssam_err(ctrl, "unexpected response from display-on notification: "
+			 "0x%02x\n", response);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int ssam_ctrl_notif_d0_exit(struct ssam_controller *ctrl)
+{
+	int status;
+	u8 response;
+
+	if (!ctrl->caps.notif_d0exit)
+		return 0;
+
+	ssam_dbg(ctrl, "pm: notifying D0 exit\n");
+
+	status = ssam_ssh_notif_d0_exit(ctrl, &response);
+	if (status)
+		return status;
+
+	if (response != 0) {
+		ssam_err(ctrl, "unexpected response from D0-exit notification: "
+			 "0x%02x\n", response);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int ssam_ctrl_notif_d0_entry(struct ssam_controller *ctrl)
+{
+	int status;
+	u8 response;
+
+	if (!ctrl->caps.notif_d0exit)
+		return 0;
+
+	ssam_dbg(ctrl, "pm: notifying D0 entry\n");
+
+	status = ssam_ssh_notif_d0_entry(ctrl, &response);
+	if (status)
+		return status;
+
+	if (response != 0) {
+		ssam_err(ctrl, "unexpected response from D0-entry notification: "
+			 "0x%02x\n", response);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+
+/* -- Top-level event registry interface. ----------------------------------- */
+
+int ssam_notifier_register(struct ssam_controller *ctrl,
+			   struct ssam_event_notifier *n)
+{
+	u16 rqid = ssh_tc_to_rqid(n->event.id.target_category);
+	struct ssam_nf_head *nf_head;
+	struct ssam_nf *nf;
+	int rc, status;
+
+	if (!ssh_rqid_is_event(rqid))
+		return -EINVAL;
+
+	nf = &ctrl->cplt.event.notif;
+	nf_head = &nf->head[ssh_rqid_to_event(rqid)];
+
+	mutex_lock(&nf->lock);
+
+	if (smp_load_acquire(&ctrl->state) != SSAM_CONTROLLER_STARTED) {
+		mutex_unlock(&nf->lock);
+		return -ENXIO;
+	}
+
+	rc = ssam_nf_refcount_inc(nf, n->event.reg, n->event.id);
+	if (rc < 0) {
+		mutex_unlock(&nf->lock);
+		return rc;
+	}
+
+	ssam_dbg(ctrl, "enabling event (reg: 0x%02x, tc: 0x%02x, iid: 0x%02x, "
+		 "rc: %d)\n", n->event.reg.target_category,
+		 n->event.id.target_category, n->event.id.instance, rc);
+
+	status = __ssam_nfblk_insert(nf_head, &n->base);
+	if (status) {
+		ssam_nf_refcount_dec(nf, n->event.reg, n->event.id);
+		mutex_unlock(&nf->lock);
+		return status;
+	}
+
+	if (rc == 1) {
+		status = ssam_ssh_event_enable(ctrl, n->event.reg, n->event.id,
+					       n->event.flags);
+		if (status) {
+			__ssam_nfblk_remove(nf_head, &n->base);
+			ssam_nf_refcount_dec(nf, n->event.reg, n->event.id);
+			mutex_unlock(&nf->lock);
+			synchronize_srcu(&nf_head->srcu);
+			return status;
+		}
+	}
+
+	mutex_unlock(&nf->lock);
+	return 0;
+
+}
+EXPORT_SYMBOL_GPL(ssam_notifier_register);
+
+int ssam_notifier_unregister(struct ssam_controller *ctrl,
+			     struct ssam_event_notifier *n)
+{
+	u16 rqid = ssh_tc_to_rqid(n->event.id.target_category);
+	struct ssam_nf_head *nf_head;
+	struct ssam_nf *nf;
+	int rc, status = 0;
+
+	if (!ssh_rqid_is_event(rqid))
+		return -EINVAL;
+
+	nf = &ctrl->cplt.event.notif;
+	nf_head = &nf->head[ssh_rqid_to_event(rqid)];
+
+	mutex_lock(&nf->lock);
+
+	if (smp_load_acquire(&ctrl->state) != SSAM_CONTROLLER_STARTED) {
+		mutex_unlock(&nf->lock);
+		return -ENXIO;
+	}
+
+	rc = ssam_nf_refcount_dec(nf, n->event.reg, n->event.id);
+	if (rc < 0) {
+		mutex_unlock(&nf->lock);
+		return rc;
+	}
+
+	ssam_dbg(ctrl, "disabling event (reg: 0x%02x, tc: 0x%02x, iid: 0x%02x, "
+		 "rc: %d)\n", n->event.reg.target_category,
+		 n->event.id.target_category, n->event.id.instance, rc);
+
+	if (rc == 0) {
+		status = ssam_ssh_event_disable(ctrl, n->event.reg, n->event.id,
+						n->event.flags);
+	}
+
+	__ssam_nfblk_remove(nf_head, &n->base);
+	mutex_unlock(&nf->lock);
+	synchronize_srcu(&nf_head->srcu);
+
+	return status;
+}
+EXPORT_SYMBOL_GPL(ssam_notifier_unregister);
+
+static bool ssam_notifier_empty(struct ssam_controller *ctrl)
+{
+	struct ssam_nf *nf = &ctrl->cplt.event.notif;
+	bool result;
+
+	mutex_lock(&nf->lock);
+	result = ssam_nf_refcount_empty(nf);
+	mutex_unlock(&nf->lock);
+
+	return result;
+}
+
+static void ssam_notifier_unregister_all(struct ssam_controller *ctrl)
+{
+	struct ssam_nf *nf = &ctrl->cplt.event.notif;
+	struct ssam_nf_refcount_entry *pos, *n;
+
+	mutex_lock(&nf->lock);
+	rbtree_postorder_for_each_entry_safe(pos, n, &nf->refcount, node) {
+		// ignore errors, will get logged in call
+		ssam_ssh_event_disable(ctrl, pos->key.reg, pos->key.id, 0);
+		kfree(pos);
+	}
+	nf->refcount = RB_ROOT;
+	mutex_unlock(&nf->lock);
+}
+
+
+/* -- Wakeup IRQ. ----------------------------------------------------------- */
+
+static const struct acpi_gpio_params gpio_ssam_wakeup_int = { 0, 0, false };
+static const struct acpi_gpio_params gpio_ssam_wakeup     = { 1, 0, false };
+
+static const struct acpi_gpio_mapping ssam_acpi_gpios[] = {
+	{ "ssam_wakeup-int-gpio", &gpio_ssam_wakeup_int, 1 },
+	{ "ssam_wakeup-gpio",     &gpio_ssam_wakeup,     1 },
+	{ },
+};
+
+static irqreturn_t ssam_irq_handle(int irq, void *dev_id)
+{
+	struct ssam_controller *ctrl = dev_id;
+
+	ssam_dbg(ctrl, "pm: wake irq triggered\n");
+
+	// Note: Proper wakeup detection is currently unimplemented.
+	//       When the EC is in display-off or any other non-D0 state, it
+	//       does not send events/notifications to the host. Instead it
+	//       signals that there are events available via the wakeup IRQ.
+	//       This driver is responsible for calling back to the EC to
+	//       release these events one-by-one.
+	//
+	//       This IRQ should not cause a full system resume by its own.
+	//       Instead, events should be handled by their respective subsystem
+	//       drivers, which in turn should signal whether a full system
+	//       resume should be performed.
+	//
+	// TODO: Send GPIO callback command repeatedly to EC until callback
+	//       returns 0x00. Return flag of callback is "has more events".
+	//       Each time the command is sent, one event is "released". Once
+	//       all events have been released (return = 0x00), the GPIO is
+	//       re-armed. Detect wakeup events during this process, go back to
+	//       sleep if no wakeup event has been received.
+
+	return IRQ_HANDLED;
+}
+
+static int ssam_irq_setup(struct ssam_controller *ctrl)
+{
+	struct device *dev = ssam_controller_device(ctrl);
+	struct gpio_desc *gpiod;
+	int irq;
+	int status;
+
+	/*
+	 * The actual GPIO interrupt is declared in ACPI as TRIGGER_HIGH.
+	 * However, the GPIO line only gets reset by sending the GPIO callback
+	 * command to SAM (or alternatively the display-on notification). As
+	 * proper handling for this interrupt is not implemented yet, leaving
+	 * the IRQ at TRIGGER_HIGH would cause an IRQ storm (as the callback
+	 * never gets sent and thus the line line never gets reset). To avoid
+	 * this, mark the IRQ as TRIGGER_RISING for now, only creating a single
+	 * interrupt, and let the SAM resume callback during the controller
+	 * resume process clear it.
+	 */
+	const int irqf = IRQF_SHARED | IRQF_ONESHOT | IRQF_TRIGGER_RISING;
+
+	gpiod = gpiod_get(dev, "ssam_wakeup-int", GPIOD_ASIS);
+	if (IS_ERR(gpiod))
+		return PTR_ERR(gpiod);
+
+	irq = gpiod_to_irq(gpiod);
+	gpiod_put(gpiod);
+
+	if (irq < 0)
+		return irq;
+
+	status = request_threaded_irq(irq, NULL, ssam_irq_handle, irqf,
+				      "surface_sam_wakeup", ctrl);
+	if (status)
+		return status;
+
+	ctrl->irq.num = irq;
+	return 0;
+}
+
+static void ssam_irq_free(struct ssam_controller *ctrl)
+{
+	free_irq(ctrl->irq.num, ctrl);
+	ctrl->irq.num = -1;
+}
+
+
+/* -- Glue layer (serdev_device -> ssam_controller). ------------------------ */
+
+static int ssam_receive_buf(struct serdev_device *dev, const unsigned char *buf,
+			    size_t n)
+{
+	struct ssam_controller *ctrl = serdev_device_get_drvdata(dev);
+	return ssam_controller_receive_buf(ctrl, buf, n);
+}
+
+static void ssam_write_wakeup(struct serdev_device *dev)
+{
+	struct ssam_controller *ctrl = serdev_device_get_drvdata(dev);
+	ssam_controller_write_wakeup(ctrl);
+}
+
+static const struct serdev_device_ops ssam_serdev_ops = {
+	.receive_buf = ssam_receive_buf,
+	.write_wakeup = ssam_write_wakeup,
+};
+
+
+/* -- ACPI based device setup. ---------------------------------------------- */
+
+static acpi_status ssam_serdev_setup_via_acpi_crs(struct acpi_resource *rsc,
+						  void *ctx)
+{
+	struct serdev_device *serdev = ctx;
+	struct acpi_resource_common_serialbus *serial;
+	struct acpi_resource_uart_serialbus *uart;
+	bool flow_control;
+	int status = 0;
+
+	if (rsc->type != ACPI_RESOURCE_TYPE_SERIAL_BUS)
+		return AE_OK;
+
+	serial = &rsc->data.common_serial_bus;
+	if (serial->type != ACPI_RESOURCE_SERIAL_TYPE_UART)
+		return AE_OK;
+
+	uart = &rsc->data.uart_serial_bus;
+
+	// set up serdev device
+	serdev_device_set_baudrate(serdev, uart->default_baud_rate);
+
+	// serdev currently only supports RTSCTS flow control
+	if (uart->flow_control & (~((u8) ACPI_UART_FLOW_CONTROL_HW))) {
+		dev_warn(&serdev->dev, "setup: unsupported flow control"
+			 " (value: 0x%02x)\n", uart->flow_control);
+	}
+
+	// set RTSCTS flow control
+	flow_control = uart->flow_control & ACPI_UART_FLOW_CONTROL_HW;
+	serdev_device_set_flow_control(serdev, flow_control);
+
+	// serdev currently only supports EVEN/ODD parity
+	switch (uart->parity) {
+	case ACPI_UART_PARITY_NONE:
+		status = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
+		break;
+	case ACPI_UART_PARITY_EVEN:
+		status = serdev_device_set_parity(serdev, SERDEV_PARITY_EVEN);
+		break;
+	case ACPI_UART_PARITY_ODD:
+		status = serdev_device_set_parity(serdev, SERDEV_PARITY_ODD);
+		break;
+	default:
+		dev_warn(&serdev->dev, "setup: unsupported parity"
+			 " (value: 0x%02x)\n", uart->parity);
+		break;
+	}
+
+	if (status) {
+		dev_err(&serdev->dev, "setup: failed to set parity"
+			" (value: 0x%02x)\n", uart->parity);
+		return status;
+	}
+
+	return AE_CTRL_TERMINATE;       // we've found the resource and are done
+}
+
+static acpi_status ssam_serdev_setup_via_acpi(acpi_handle handle,
+					      struct serdev_device *serdev)
+{
+	return acpi_walk_resources(handle, METHOD_NAME__CRS,
+				   ssam_serdev_setup_via_acpi_crs, serdev);
+}
+
+
+/* -- Power management. ----------------------------------------------------- */
+
+static void surface_sam_ssh_shutdown(struct device *dev)
+{
+	struct ssam_controller *c = dev_get_drvdata(dev);
+	int status;
+
+	/*
+	 * Try to signal display-off and D0-exit, ignore any errors.
+	 *
+	 * Note: It has not been established yet if this is actually
+	 * necessary/useful for shutdown.
+	 */
+
+	status = ssam_ctrl_notif_display_off(c);
+	if (status)
+		ssam_err(c, "pm: display-off notification failed: %d\n", status);
+
+	status = ssam_ctrl_notif_d0_exit(c);
+	if (status)
+		ssam_err(c, "pm: D0-exit notification failed: %d\n", status);
+}
+
+static int surface_sam_ssh_suspend(struct device *dev)
+{
+	struct ssam_controller *c = dev_get_drvdata(dev);
+	int status;
+
+	/*
+	 * Try to signal display-off and D0-exit, enable IRQ wakeup if
+	 * specified. Abort on error.
+	 *
+	 * Note: Signalling display-off/display-on should normally be done from
+	 * some sort of display state notifier. As that is not available, signal
+	 * it here.
+	 */
+
+	status = ssam_ctrl_notif_display_off(c);
+	if (status) {
+		ssam_err(c, "pm: display-off notification failed: %d\n", status);
+		return status;
+	}
+
+	status = ssam_ctrl_notif_d0_exit(c);
+	if (status) {
+		ssam_err(c, "pm: D0-exit notification failed: %d\n", status);
+		goto err_notif;
+	}
+
+	if (device_may_wakeup(dev)) {
+		status = enable_irq_wake(c->irq.num);
+		if (status) {
+			ssam_err(c, "failed to disable wake IRQ: %d\n", status);
+			goto err_irq;
+		}
+
+		c->irq.wakeup_enabled = true;
+	} else {
+		c->irq.wakeup_enabled = false;
+	}
+
+	WARN_ON(ssam_controller_suspend(c));
+	return 0;
+
+err_irq:
+	ssam_ctrl_notif_d0_entry(c);
+err_notif:
+	ssam_ctrl_notif_display_on(c);
+	return status;
+}
+
+static int surface_sam_ssh_resume(struct device *dev)
+{
+	struct ssam_controller *c = dev_get_drvdata(dev);
+	int status;
+
+	WARN_ON(ssam_controller_resume(c));
+
+	/*
+	 * Try to disable IRQ wakeup (if specified), signal display-on and
+	 * D0-entry. In case of errors, log them and try to restore normal
+	 * operation state as far as possible.
+	 *
+	 * Note: Signalling display-off/display-on should normally be done from
+	 * some sort of display state notifier. As that is not available, signal
+	 * it here.
+	 */
+
+	if (c->irq.wakeup_enabled) {
+		status = disable_irq_wake(c->irq.num);
+		if (status)
+			ssam_err(c, "failed to disable wake IRQ: %d\n", status);
+
+		c->irq.wakeup_enabled = false;
+	}
+
+	status = ssam_ctrl_notif_d0_entry(c);
+	if (status)
+		ssam_err(c, "pm: display-on notification failed: %d\n", status);
+
+	status = ssam_ctrl_notif_display_on(c);
+	if (status)
+		ssam_err(c, "pm: D0-entry notification failed: %d\n", status);
+
+	return 0;
+}
+
+static SIMPLE_DEV_PM_OPS(surface_sam_ssh_pm_ops, surface_sam_ssh_suspend,
+			 surface_sam_ssh_resume);
+
+
+/* -- Device/driver setup. -------------------------------------------------- */
+
+static struct ssam_controller ssam_controller = {
+	.state = SSAM_CONTROLLER_UNINITIALIZED,
+};
+static DEFINE_MUTEX(ssam_controller_lock);
+
+static int __ssam_client_link(struct ssam_controller *c, struct device *client)
+{
+	const u32 flags = DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
+	struct device_link *link;
+	struct device *ctrldev;
+
+	if (smp_load_acquire(&c->state) != SSAM_CONTROLLER_STARTED)
+		return -ENXIO;
+
+	if ((ctrldev = ssam_controller_device(c)) == NULL)
+		return -ENXIO;
+
+	if ((link = device_link_add(client, ctrldev, flags)) == NULL)
+		return -ENOMEM;
+
+	/*
+	 * Return -ENXIO if supplier driver is on its way to be removed. In this
+	 * case, the controller won't be around for much longer and the device
+	 * link is not going to save us any more, as unbinding is already in
+	 * progress.
+	 */
+	if (link->status == DL_STATE_SUPPLIER_UNBIND)
+		return -ENXIO;
+
+	return 0;
+}
+
+int ssam_client_bind(struct device *client, struct ssam_controller **ctrl)
+{
+	struct ssam_controller *c = &ssam_controller;
+	int status;
+
+	mutex_lock(&ssam_controller_lock);
+	status = __ssam_client_link(c, client);
+	mutex_unlock(&ssam_controller_lock);
+
+	*ctrl = status == 0 ? c : NULL;
+	return status;
+}
+EXPORT_SYMBOL_GPL(ssam_client_bind);
+
+
+static int surface_sam_ssh_probe(struct serdev_device *serdev)
+{
+	struct ssam_controller *ctrl = &ssam_controller;
+	acpi_handle *ssh = ACPI_HANDLE(&serdev->dev);
+	int status;
+
+	if (gpiod_count(&serdev->dev, NULL) < 0)
+		return -ENODEV;
+
+	status = devm_acpi_dev_add_driver_gpios(&serdev->dev, ssam_acpi_gpios);
+	if (status)
+		return status;
+
+	// set up EC
+	mutex_lock(&ssam_controller_lock);
+
+	// initialize controller
+	status = ssam_controller_init(ctrl, serdev);
+	if (status)
+		goto err_ctrl_init;
+
+	// set up serdev device
+	serdev_device_set_drvdata(serdev, ctrl);
+	serdev_device_set_client_ops(serdev, &ssam_serdev_ops);
+	status = serdev_device_open(serdev);
+	if (status)
+		goto err_devopen;
+
+	status = ssam_serdev_setup_via_acpi(ssh, serdev);
+	if (ACPI_FAILURE(status))
+		goto err_devinit;
+
+	// start controller
+	status = ssam_controller_start(ctrl);
+	if (status)
+		goto err_devinit;
+
+	// initial SAM requests: log version, notify default/init power states
+	status = ssam_log_firmware_version(ctrl);
+	if (status)
+		goto err_initrq;
+
+	status = ssam_ctrl_notif_d0_entry(ctrl);
+	if (status)
+		goto err_initrq;
+
+	status = ssam_ctrl_notif_display_on(ctrl);
+	if (status)
+		goto err_initrq;
+
+	// setup IRQ
+	status = ssam_irq_setup(ctrl);
+	if (status)
+		goto err_initrq;
+
+	mutex_unlock(&ssam_controller_lock);
+
+	/*
+	 * TODO: The EC can wake up the system via the associated GPIO interrupt
+	 *       in multiple situations. One of which is the remaining battery
+	 *       capacity falling below a certain threshold. Normally, we should
+	 *       use the device_init_wakeup function, however, the EC also seems
+	 *       to have other reasons for waking up the system and it seems
+	 *       that Windows has additional checks whether the system should be
+	 *       resumed. In short, this causes some spurious unwanted wake-ups.
+	 *       For now let's thus default power/wakeup to false.
+	 */
+	device_set_wakeup_capable(&serdev->dev, true);
+	acpi_walk_dep_device_list(ssh);
+
+	return 0;
+
+err_initrq:
+	ssam_controller_shutdown(ctrl);
+err_devinit:
+	serdev_device_close(serdev);
+err_devopen:
+	ssam_controller_destroy(ctrl);
+err_ctrl_init:
+	serdev_device_set_drvdata(serdev, NULL);
+	mutex_unlock(&ssam_controller_lock);
+	return status;
+}
+
+static void surface_sam_ssh_remove(struct serdev_device *serdev)
+{
+	struct ssam_controller *ctrl = serdev_device_get_drvdata(serdev);
+	int status;
+
+	mutex_lock(&ssam_controller_lock);
+	ssam_irq_free(ctrl);
+
+	// suspend EC and disable events
+	status = ssam_ctrl_notif_display_off(ctrl);
+	if (status) {
+		dev_err(&serdev->dev, "display-off notification failed: %d\n",
+			status);
+	}
+
+	status = ssam_ctrl_notif_d0_exit(ctrl);
+	if (status) {
+		dev_err(&serdev->dev, "D0-exit notification failed: %d\n",
+			status);
+	}
+
+	ssam_controller_shutdown(ctrl);
+
+	// shut down actual transport
+	serdev_device_wait_until_sent(serdev, 0);
+	serdev_device_close(serdev);
+
+	ssam_controller_destroy(ctrl);
+
+	device_set_wakeup_capable(&serdev->dev, false);
+	serdev_device_set_drvdata(serdev, NULL);
+	mutex_unlock(&ssam_controller_lock);
+}
+
+
+static const struct acpi_device_id surface_sam_ssh_match[] = {
+	{ "MSHW0084", 0 },
+	{ },
+};
+MODULE_DEVICE_TABLE(acpi, surface_sam_ssh_match);
+
+static struct serdev_device_driver surface_sam_ssh = {
+	.probe = surface_sam_ssh_probe,
+	.remove = surface_sam_ssh_remove,
+	.driver = {
+		.name = "surface_sam_ssh",
+		.acpi_match_table = surface_sam_ssh_match,
+		.pm = &surface_sam_ssh_pm_ops,
+		.shutdown = surface_sam_ssh_shutdown,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+
+
+/* -- Module setup. --------------------------------------------------------- */
+
+static int __init surface_sam_ssh_init(void)
+{
+	int status;
+
+	status = ssh_ctrl_packet_cache_init();
+	if (status)
+		goto err_cpkg;
+
+	status = ssam_event_item_cache_init();
+	if (status)
+		goto err_evitem;
+
+	status = serdev_device_driver_register(&surface_sam_ssh);
+	if (status)
+		goto err_register;
+
+	return 0;
+
+err_register:
+	ssam_event_item_cache_destroy();
+err_evitem:
+	ssh_ctrl_packet_cache_destroy();
+err_cpkg:
+	return status;
+}
+
+static void __exit surface_sam_ssh_exit(void)
+{
+	serdev_device_driver_unregister(&surface_sam_ssh);
+	ssam_event_item_cache_destroy();
+	ssh_ctrl_packet_cache_destroy();
+}
+
+/*
+ * Ensure that the driver is loaded late due to some issues with the UART
+ * communication. Specifically, we want to ensure that DMA is ready and being
+ * used. Not using DMA can result in spurious communication failures,
+ * especially during boot, which among other things will result in wrong
+ * battery information (via ACPI _BIX) being displayed. Using a late init_call
+ * instead of the normal module_init gives the DMA subsystem time to
+ * initialize and via that results in a more stable communication, avoiding
+ * such failures.
+ */
+late_initcall(surface_sam_ssh_init);
+module_exit(surface_sam_ssh_exit);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("Surface Serial Hub Driver for 5th Generation Surface Devices");
+MODULE_LICENSE("GPL");
diff --git a/drivers/platform/x86/surface_sam/surface_sam_ssh.h b/drivers/platform/x86/surface_sam/surface_sam_ssh.h
new file mode 100644
index 000000000000..ba57adb2a3c9
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_ssh.h
@@ -0,0 +1,717 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Interface for Surface Serial Hub (SSH).
+ *
+ * The SSH is the main communication hub for communication between host and
+ * the Surface/System Aggregator Module (SAM) on newer Microsoft Surface
+ * devices (Book 2, Pro 5, Laptops, ...). Also referred to as SAM-over-SSH.
+ * Older devices (Book 1, Pro 4) use SAM-over-HID (via I2C).
+ */
+
+#ifndef _SURFACE_SAM_SSH_H
+#define _SURFACE_SAM_SSH_H
+
+#include <linux/types.h>
+#include <linux/device.h>
+
+
+/* -- Data structures for SAM-over-SSH communication. ----------------------- */
+
+/**
+ * enum ssh_frame_type - Frame types for SSH frames.
+ * @SSH_FRAME_TYPE_DATA_SEQ: Indicates a data frame, followed by a payload with
+ *                      the length specified in the ssh_frame.len field. This
+ *                      frame is sequenced, meaning that an ACK is required.
+ * @SSH_FRAME_TYPE_DATA_NSQ: Same as SSH_FRAME_TYPE_DATA_SEQ, but unsequenced,
+ *                      meaning that the message does not have to be ACKed.
+ * @SSH_FRAME_TYPE_ACK: Indicates an ACK message.
+ * @SSH_FRAME_TYPE_NAK: Indicates an error response for previously sent
+ *                      frame. In general, this means that the frame and/or
+ *                      payload is malformed, e.g. a CRC is wrong. For command-
+ *                      type payloads, this can also mean that the command is
+ *                      invalid.
+ */
+enum ssh_frame_type {
+	SSH_FRAME_TYPE_DATA_SEQ = 0x80,
+	SSH_FRAME_TYPE_DATA_NSQ = 0x00,
+	SSH_FRAME_TYPE_ACK	= 0x40,
+	SSH_FRAME_TYPE_NAK	= 0x04,
+};
+
+/**
+ * struct ssh_frame - SSH communication frame.
+ * @type: The type of the frame. See &enum ssh_frame_type.
+ * @len:  The length of the frame payload directly following the CRC for this
+ *        frame. Does not include the final CRC for that payload.
+ * @seq:  The sequence number for this message/exchange.
+ */
+struct ssh_frame {
+	u8 type;
+	__le16 len;
+	u8 seq;
+} __packed;
+
+static_assert(sizeof(struct ssh_frame) == 4);
+
+/*
+ * Maximum SSH frame payload length in bytes. This is the physical maximum
+ * length of the protocol. Implementations may set a more constrained limit.
+ */
+#define SSH_FRAME_MAX_PAYLOAD_SIZE	U16_MAX
+
+/**
+ * enum ssh_payload_type - Type indicator for the SSH payload.
+ * @SSH_PLD_TYPE_CMD: The payload is a command structure with optional command
+ *                    payload.
+ */
+enum ssh_payload_type {
+	SSH_PLD_TYPE_CMD = 0x80,
+};
+
+/**
+ * struct ssh_command - Payload of a command-type frame.
+ * @type:    The type of the payload. See &enum ssh_payload_type. Should be
+ *           SSH_PLD_TYPE_CMD for this struct.
+ * @tc:      Command target category.
+ * @chn_out: Output channel. Should be zero if this an incoming (EC to host)
+ *           message.
+ * @chn_in:  Input channel. Should be zero if this is an outgoing (hos to EC)
+ *           message.
+ * @iid:     Instance ID.
+ * @rqid:    Request ID. Used to match requests with responses and differentiate
+ *           between responses and events.
+ * @cid:     Command ID.
+ */
+struct ssh_command {
+	u8 type;
+	u8 tc;
+	u8 chn_out;
+	u8 chn_in;
+	u8 iid;
+	__le16 rqid;
+	u8 cid;
+} __packed;
+
+static_assert(sizeof(struct ssh_command) == 8);
+
+/*
+ * Maximum SSH command payload length in bytes. This is the physical maximum
+ * length of the protocol. Implementations may set a more constrained limit.
+ */
+#define SSH_COMMAND_MAX_PAYLOAD_SIZE \
+	(SSH_FRAME_MAX_PAYLOAD_SIZE - sizeof(struct ssh_command))
+
+/**
+ * struct ssh_notification_params - Command payload to enable/disable SSH
+ * notifications.
+ * @target_category: The target category for which notifications should be
+ *                   enabled/disabled.
+ * @flags:           Flags determining how notifications are being sent.
+ * @request_id:      The request ID that is used to send these notifications.
+ * @instance_id:     The specific instance in the given target category for
+ *                   which notifications should be enabled.
+ */
+struct ssh_notification_params {
+	u8 target_category;
+	u8 flags;
+	__le16 request_id;
+	u8 instance_id;
+} __packed;
+
+static_assert(sizeof(struct ssh_notification_params) == 5);
+
+/**
+ * SSH message syncrhonization (SYN) bytes.
+ */
+#define SSH_MSG_SYN		((u16)0x55aa)
+
+/**
+ * Base-length of a SSH message. This is the minimum number of bytes required
+ * to form a message. The actual message length is SSH_MSG_LEN_BASE plus the
+ * length of the frame payload.
+ */
+#define SSH_MSG_LEN_BASE	(sizeof(struct ssh_frame) + 3ull * sizeof(u16))
+
+/**
+ * Length of a SSH control message.
+ */
+#define SSH_MSG_LEN_CTRL	SSH_MSG_LEN_BASE
+
+/**
+ * Length of a SSH message with payload of specified size.
+ */
+#define SSH_MESSAGE_LENGTH(payload_size) (SSH_MSG_LEN_BASE + payload_size)
+
+/**
+ * Length of a SSH command message with command payload of specified size.
+ */
+#define SSH_COMMAND_MESSAGE_LENGTH(payload_size) \
+	SSH_MESSAGE_LENGTH(sizeof(struct ssh_command) + payload_size)
+
+/**
+ * Offset of the specified struct ssh_frame field in the raw SSH message data.
+ */
+#define SSH_MSGOFFSET_FRAME(field) \
+	(sizeof(u16) + offsetof(struct ssh_frame, field))
+
+/**
+ * Offset of the specified struct ssh_command field in the raw SSH message data.
+ */
+#define SSH_MSGOFFSET_COMMAND(field) \
+	(2ull * sizeof(u16) + sizeof(struct ssh_frame) \
+		+ offsetof(struct ssh_command, field))
+
+/**
+ * struct ssam_span - reference to a buffer region
+ * @ptr: pointer to the buffer region
+ * @len: length of the buffer region
+ *
+ * A reference to a (non-owned) buffer segment, consisting of pointer and
+ * length. Use of this struct indicates non-owned data, i.e. data of which the
+ * life-time is managed (i.e. it is allocated/freed) via another pointer.
+ */
+struct ssam_span {
+	u8    *ptr;
+	size_t len;
+};
+
+
+/* -- Packet transport layer (ptl). ----------------------------------------- */
+
+enum ssh_packet_priority {
+	SSH_PACKET_PRIORITY_FLUSH = 0,
+	SSH_PACKET_PRIORITY_DATA  = 0,
+	SSH_PACKET_PRIORITY_NAK   = 1 << 4,
+	SSH_PACKET_PRIORITY_ACK   = 2 << 4,
+};
+
+#define SSH_PACKET_PRIORITY(base, try) \
+	((SSH_PACKET_PRIORITY_##base) | ((try) & 0x0f))
+
+#define ssh_packet_priority_get_try(p) ((p) & 0x0f)
+
+
+enum ssh_packet_flags {
+	SSH_PACKET_SF_LOCKED_BIT,
+	SSH_PACKET_SF_QUEUED_BIT,
+	SSH_PACKET_SF_PENDING_BIT,
+	SSH_PACKET_SF_TRANSMITTING_BIT,
+	SSH_PACKET_SF_TRANSMITTED_BIT,
+	SSH_PACKET_SF_ACKED_BIT,
+	SSH_PACKET_SF_CANCELED_BIT,
+	SSH_PACKET_SF_COMPLETED_BIT,
+
+	SSH_PACKET_TY_FLUSH_BIT,
+	SSH_PACKET_TY_SEQUENCED_BIT,
+	SSH_PACKET_TY_BLOCKING_BIT,
+
+	SSH_PACKET_FLAGS_SF_MASK =
+		  BIT(SSH_PACKET_SF_LOCKED_BIT)
+		| BIT(SSH_PACKET_SF_QUEUED_BIT)
+		| BIT(SSH_PACKET_SF_PENDING_BIT)
+		| BIT(SSH_PACKET_SF_TRANSMITTING_BIT)
+		| BIT(SSH_PACKET_SF_TRANSMITTED_BIT)
+		| BIT(SSH_PACKET_SF_ACKED_BIT)
+		| BIT(SSH_PACKET_SF_CANCELED_BIT)
+		| BIT(SSH_PACKET_SF_COMPLETED_BIT),
+
+	SSH_PACKET_FLAGS_TY_MASK =
+		  BIT(SSH_PACKET_TY_FLUSH_BIT)
+		| BIT(SSH_PACKET_TY_SEQUENCED_BIT)
+		| BIT(SSH_PACKET_TY_BLOCKING_BIT),
+};
+
+
+struct ssh_ptl;
+struct ssh_packet;
+
+struct ssh_packet_ops {
+	void (*release)(struct ssh_packet *p);
+	void (*complete)(struct ssh_packet *p, int status);
+};
+
+struct ssh_packet {
+	struct ssh_ptl *ptl;
+	struct kref refcnt;
+
+	u8 priority;
+
+	struct {
+		size_t len;
+		u8 *ptr;
+	} data;
+
+	unsigned long state;
+	ktime_t timestamp;
+
+	struct list_head queue_node;
+	struct list_head pending_node;
+
+	const struct ssh_packet_ops *ops;
+};
+
+
+void ssh_packet_get(struct ssh_packet *p);
+void ssh_packet_put(struct ssh_packet *p);
+
+static inline void ssh_packet_set_data(struct ssh_packet *p, u8 *ptr, size_t len)
+{
+	p->data.ptr = ptr;
+	p->data.len = len;
+}
+
+
+/* -- Request transport layer (rtl). ---------------------------------------- */
+
+enum ssh_request_flags {
+	SSH_REQUEST_SF_LOCKED_BIT,
+	SSH_REQUEST_SF_QUEUED_BIT,
+	SSH_REQUEST_SF_PENDING_BIT,
+	SSH_REQUEST_SF_TRANSMITTING_BIT,
+	SSH_REQUEST_SF_TRANSMITTED_BIT,
+	SSH_REQUEST_SF_RSPRCVD_BIT,
+	SSH_REQUEST_SF_CANCELED_BIT,
+	SSH_REQUEST_SF_COMPLETED_BIT,
+
+	SSH_REQUEST_TY_FLUSH_BIT,
+	SSH_REQUEST_TY_HAS_RESPONSE_BIT,
+
+	SSH_REQUEST_FLAGS_SF_MASK =
+		  BIT(SSH_REQUEST_SF_LOCKED_BIT)
+		| BIT(SSH_REQUEST_SF_QUEUED_BIT)
+		| BIT(SSH_REQUEST_SF_PENDING_BIT)
+		| BIT(SSH_REQUEST_SF_TRANSMITTING_BIT)
+		| BIT(SSH_REQUEST_SF_TRANSMITTED_BIT)
+		| BIT(SSH_REQUEST_SF_RSPRCVD_BIT)
+		| BIT(SSH_REQUEST_SF_CANCELED_BIT)
+		| BIT(SSH_REQUEST_SF_COMPLETED_BIT),
+
+	SSH_REQUEST_FLAGS_TY_MASK =
+		  BIT(SSH_REQUEST_TY_FLUSH_BIT)
+		| BIT(SSH_REQUEST_TY_HAS_RESPONSE_BIT),
+};
+
+
+struct ssh_rtl;
+struct ssh_request;
+
+struct ssh_request_ops {
+	void (*release)(struct ssh_request *rqst);
+	void (*complete)(struct ssh_request *rqst,
+			 const struct ssh_command *cmd,
+			 const struct ssam_span *data, int status);
+};
+
+struct ssh_request {
+	struct ssh_packet packet;
+	struct list_head node;
+
+	unsigned long state;
+	ktime_t timestamp;
+
+	const struct ssh_request_ops *ops;
+};
+
+
+static inline void ssh_request_get(struct ssh_request *r)
+{
+	ssh_packet_get(&r->packet);
+}
+
+static inline void ssh_request_put(struct ssh_request *r)
+{
+	ssh_packet_put(&r->packet);
+}
+
+static inline void ssh_request_set_data(struct ssh_request *r, u8 *ptr, size_t len)
+{
+	ssh_packet_set_data(&r->packet, ptr, len);
+}
+
+
+/* -- Main data types and definitions --------------------------------------- */
+
+enum ssam_ssh_tc {
+	SSAM_SSH_TC_SAM = 0x01,	// generic system functionality, real-time clock
+	SSAM_SSH_TC_BAT = 0x02,	// battery/power subsystem
+	SSAM_SSH_TC_TMP = 0x03,	// thermal subsystem
+	SSAM_SSH_TC_PMC = 0x04,
+	SSAM_SSH_TC_FAN = 0x05,
+	SSAM_SSH_TC_PoM = 0x06,
+	SSAM_SSH_TC_DBG = 0x07,
+	SSAM_SSH_TC_KBD = 0x08,	// legacy keyboard (Laptop 1/2)
+	SSAM_SSH_TC_FWU = 0x09,
+	SSAM_SSH_TC_UNI = 0x0a,
+	SSAM_SSH_TC_LPC = 0x0b,
+	SSAM_SSH_TC_TCL = 0x0c,
+	SSAM_SSH_TC_SFL = 0x0d,
+	SSAM_SSH_TC_KIP = 0x0e,
+	SSAM_SSH_TC_EXT = 0x0f,
+	SSAM_SSH_TC_BLD = 0x10,
+	SSAM_SSH_TC_BAS = 0x11,	// detachment system (Surface Book 2/3)
+	SSAM_SSH_TC_SEN = 0x12,
+	SSAM_SSH_TC_SRQ = 0x13,
+	SSAM_SSH_TC_MCU = 0x14,
+	SSAM_SSH_TC_HID = 0x15,	// generic HID input subsystem
+	SSAM_SSH_TC_TCH = 0x16,
+	SSAM_SSH_TC_BKL = 0x17,
+	SSAM_SSH_TC_TAM = 0x18,
+	SSAM_SSH_TC_ACC = 0x19,
+	SSAM_SSH_TC_UFI = 0x1a,
+	SSAM_SSH_TC_USC = 0x1b,
+	SSAM_SSH_TC_PEN = 0x1c,
+	SSAM_SSH_TC_VID = 0x1d,
+	SSAM_SSH_TC_AUD = 0x1e,
+	SSAM_SSH_TC_SMC = 0x1f,
+	SSAM_SSH_TC_KPD = 0x20,
+	SSAM_SSH_TC_REG = 0x21,
+};
+
+struct ssam_controller;
+
+/**
+ * struct ssam_event_flags - Flags for enabling/disabling SAM-over-SSH events
+ * @SSAM_EVENT_SEQUENCED: The event will be sent via a sequenced data frame.
+ */
+enum ssam_event_flags {
+	SSAM_EVENT_SEQUENCED = BIT(0),
+};
+
+struct ssam_event {
+	u8 target_category;
+	u8 command_id;
+	u8 instance_id;
+	u8 channel;
+	u16 length;
+	u8 data[0];
+};
+
+enum ssam_request_flags {
+	SSAM_REQUEST_HAS_RESPONSE = BIT(0),
+	SSAM_REQUEST_UNSEQUENCED  = BIT(1),
+};
+
+struct ssam_request {
+	u8 target_category;
+	u8 command_id;
+	u8 instance_id;
+	u8 channel;
+	u16 flags;
+	u16 length;
+	const u8 *payload;
+};
+
+struct ssam_response {
+	size_t capacity;
+	size_t length;
+	u8 *pointer;
+};
+
+
+int ssam_client_bind(struct device *client, struct ssam_controller **ctrl);
+
+struct device *ssam_controller_device(struct ssam_controller *c);
+
+ssize_t ssam_request_write_data(struct ssam_span *buf,
+				struct ssam_controller *ctrl,
+				struct ssam_request *spec);
+
+
+/* -- Synchronous request interface. ---------------------------------------- */
+
+struct ssam_request_sync {
+	struct ssh_request base;
+	struct completion comp;
+	struct ssam_response *resp;
+	int status;
+};
+
+int ssam_request_sync_alloc(size_t payload_len, gfp_t flags,
+			    struct ssam_request_sync **rqst,
+			    struct ssam_span *buffer);
+
+void ssam_request_sync_init(struct ssam_request_sync *rqst,
+			    enum ssam_request_flags flags);
+
+static inline void ssam_request_sync_set_data(struct ssam_request_sync *rqst,
+					      u8 *ptr, size_t len)
+{
+	ssh_request_set_data(&rqst->base, ptr, len);
+}
+
+static inline void ssam_request_sync_set_resp(struct ssam_request_sync *rqst,
+					      struct ssam_response *resp)
+{
+	rqst->resp = resp;
+}
+
+int ssam_request_sync_submit(struct ssam_controller *ctrl,
+			     struct ssam_request_sync *rqst);
+
+static inline int ssam_request_sync_wait(struct ssam_request_sync *rqst)
+{
+	wait_for_completion(&rqst->comp);
+	return rqst->status;
+}
+
+int ssam_request_sync(struct ssam_controller *ctrl, struct ssam_request *spec,
+		      struct ssam_response *rsp);
+
+int ssam_request_sync_with_buffer(struct ssam_controller *ctrl,
+				  struct ssam_request *spec,
+				  struct ssam_response *rsp,
+				  struct ssam_span *buf);
+
+
+#define ssam_request_sync_onstack(ctrl, rqst, rsp, payload_len)			\
+	({									\
+		u8 __data[SSH_COMMAND_MESSAGE_LENGTH(payload_len)];		\
+		struct ssam_span __buf = { &__data[0], ARRAY_SIZE(__data) };	\
+		int __status;							\
+										\
+		/* ensure input does not overflow buffer */			\
+		if ((rqst)->length <= payload_len) {				\
+			__status = ssam_request_sync_with_buffer(		\
+					ctrl, rqst, rsp, &__buf);		\
+		} else {							\
+			__status = -EINVAL;					\
+		}								\
+										\
+		__status;							\
+	})
+
+
+struct ssam_request_spec {
+	u8 target_category;
+	u8 command_id;
+	u8 instance_id;
+	u8 channel;
+	u8 flags;
+};
+
+struct ssam_request_spec_md {
+	u8 target_category;
+	u8 command_id;
+	u8 flags;
+};
+
+#define SSAM_DEFINE_SYNC_REQUEST_N(name, spec...)				\
+	int name(struct ssam_controller *ctrl)					\
+	{									\
+		struct ssam_request_spec s = (struct ssam_request_spec)spec;	\
+		struct ssam_request rqst;					\
+										\
+		rqst.target_category = s.target_category;			\
+		rqst.command_id = s.command_id;					\
+		rqst.instance_id = s.instance_id;				\
+		rqst.channel = s.channel;					\
+		rqst.flags = s.flags;						\
+		rqst.length = 0;						\
+		rqst.payload = NULL;						\
+										\
+		return ssam_request_sync_onstack(ctrl, &rqst, NULL, 0);		\
+	}
+
+#define SSAM_DEFINE_SYNC_REQUEST_W(name, wtype, spec...)			\
+	int name(struct ssam_controller *ctrl, const wtype *in)			\
+	{									\
+		struct ssam_request_spec s = (struct ssam_request_spec)spec;	\
+		struct ssam_request rqst;					\
+										\
+		rqst.target_category = s.target_category;			\
+		rqst.command_id = s.command_id;					\
+		rqst.instance_id = s.instance_id;				\
+		rqst.channel = s.channel;					\
+		rqst.flags = s.flags;						\
+		rqst.length = sizeof(wtype);					\
+		rqst.payload = (u8 *)in;					\
+										\
+		return ssam_request_sync_onstack(ctrl, &rqst, NULL,		\
+						 sizeof(wtype));		\
+	}
+
+#define SSAM_DEFINE_SYNC_REQUEST_R(name, rtype, spec...)			\
+	int name(struct ssam_controller *ctrl, rtype *out)			\
+	{									\
+		struct ssam_request_spec s = (struct ssam_request_spec)spec;	\
+		struct ssam_request rqst;					\
+		struct ssam_response rsp;					\
+		int status;							\
+										\
+		rqst.target_category = s.target_category;			\
+		rqst.command_id = s.command_id;					\
+		rqst.instance_id = s.instance_id;				\
+		rqst.channel = s.channel;					\
+		rqst.flags = s.flags | SSAM_REQUEST_HAS_RESPONSE;		\
+		rqst.length = 0;						\
+		rqst.payload = NULL;						\
+										\
+		rsp.capacity = sizeof(rtype);					\
+		rsp.length = 0;							\
+		rsp.pointer = (u8 *)out;					\
+										\
+		status = ssam_request_sync_onstack(ctrl, &rqst, &rsp, 0);	\
+		if (status)							\
+			return status;						\
+										\
+		if (rsp.length != sizeof(rtype)) {				\
+			struct device *dev = ssam_controller_device(ctrl);	\
+			dev_err(dev, "rqst: invalid response length, expected %zu, got %zu" \
+				" (tc: 0x%02x, cid: 0x%02x)", sizeof(rtype),	\
+				rsp.length, rqst.target_category,		\
+				rqst.command_id);				\
+			return -EIO;						\
+		}								\
+										\
+		return 0;							\
+	}
+
+#define SSAM_DEFINE_SYNC_REQUEST_MD_W(name, wtype, spec...)			\
+	int name(struct ssam_controller *ctrl, u8 chn, u8 iid, const wtype *in)	\
+	{									\
+		struct ssam_request_spec_md s					\
+			= (struct ssam_request_spec_md)spec;			\
+		struct ssam_request rqst;					\
+										\
+		rqst.target_category = s.target_category;			\
+		rqst.command_id = s.command_id;					\
+		rqst.instance_id = iid;						\
+		rqst.channel = chn;						\
+		rqst.flags = s.flags;						\
+		rqst.length = sizeof(wtype);					\
+		rqst.payload = (u8 *)in;					\
+										\
+		return ssam_request_sync_onstack(ctrl, &rqst, NULL,		\
+						 sizeof(wtype));		\
+	}
+
+#define SSAM_DEFINE_SYNC_REQUEST_MD_R(name, rtype, spec...)			\
+	int name(struct ssam_controller *ctrl, u8 chn, u8 iid, rtype *out)	\
+	{									\
+		struct ssam_request_spec_md s					\
+			= (struct ssam_request_spec_md)spec;			\
+		struct ssam_request rqst;					\
+		struct ssam_response rsp;					\
+		int status;							\
+										\
+		rqst.target_category = s.target_category;			\
+		rqst.command_id = s.command_id;					\
+		rqst.instance_id = iid;						\
+		rqst.channel = chn;						\
+		rqst.flags = s.flags | SSAM_REQUEST_HAS_RESPONSE;		\
+		rqst.length = 0;						\
+		rqst.payload = NULL;						\
+										\
+		rsp.capacity = sizeof(rtype);					\
+		rsp.length = 0;							\
+		rsp.pointer = (u8 *)out;					\
+										\
+		status = ssam_request_sync_onstack(ctrl, &rqst, &rsp, 0);	\
+		if (status)							\
+			return status;						\
+										\
+		if (rsp.length != sizeof(rtype)) {				\
+			struct device *dev = ssam_controller_device(ctrl);	\
+			dev_err(dev, "rqst: invalid response length, expected %zu, got %zu" \
+				" (tc: 0x%02x, cid: 0x%02x)", sizeof(rtype),	\
+				rsp.length, rqst.target_category,		\
+				rqst.command_id);				\
+			return -EIO;						\
+		}								\
+										\
+		return 0;							\
+	}
+
+
+/* -- Event notifier/callbacks. --------------------------------------------- */
+
+#define SSAM_NOTIF_STATE_SHIFT		2
+#define SSAM_NOTIF_STATE_MASK		((1 << SSAM_NOTIF_STATE_SHIFT) - 1)
+
+#define SSAM_NOTIF_HANDLED		BIT(0)
+#define SSAM_NOTIF_STOP			BIT(1)
+
+
+struct ssam_notifier_block;
+
+typedef u32 (*ssam_notifier_fn_t)(struct ssam_notifier_block *nb,
+				  const struct ssam_event *event);
+
+struct ssam_notifier_block {
+	struct ssam_notifier_block __rcu *next;
+	ssam_notifier_fn_t fn;
+	int priority;
+};
+
+
+static inline u32 ssam_notifier_from_errno(int err)
+{
+	if (WARN_ON(err > 0) || err == 0)
+		return 0;
+	else
+		return ((-err) << SSAM_NOTIF_STATE_SHIFT) | SSAM_NOTIF_STOP;
+}
+
+static inline int ssam_notifier_to_errno(u32 ret)
+{
+	return -(ret >> SSAM_NOTIF_STATE_SHIFT);
+}
+
+
+/* -- Event/notification registry. ------------------------------------------ */
+
+struct ssam_event_registry {
+	u8 target_category;
+	u8 channel;
+	u8 cid_enable;
+	u8 cid_disable;
+};
+
+struct ssam_event_id {
+	u8 target_category;
+	u8 instance;
+};
+
+
+#define SSAM_EVENT_REGISTRY(tc, chn, cid_en, cid_dis)	\
+	((struct ssam_event_registry) {			\
+		.target_category = (tc),		\
+		.channel = (chn),			\
+		.cid_enable = (cid_en),			\
+		.cid_disable = (cid_dis),		\
+	})
+
+#define SSAM_EVENT_ID(tc, iid)				\
+	((struct ssam_event_id) {			\
+		.target_category = tc,			\
+		.instance = iid,			\
+	})
+
+
+#define SSAM_EVENT_REGISTRY_SAM	\
+	SSAM_EVENT_REGISTRY(SSAM_SSH_TC_SAM, 0x01, 0x0b, 0x0c)
+
+#define SSAM_EVENT_REGISTRY_KIP	\
+	SSAM_EVENT_REGISTRY(SSAM_SSH_TC_KIP, 0x02, 0x27, 0x28)
+
+#define SSAM_EVENT_REGISTRY_REG \
+	SSAM_EVENT_REGISTRY(SSAM_SSH_TC_REG, 0x02, 0x01, 0x02)
+
+
+struct ssam_event_notifier {
+	struct ssam_notifier_block base;
+
+	struct {
+		struct ssam_event_registry reg;
+		struct ssam_event_id id;
+		u8 flags;
+	} event;
+};
+
+int ssam_notifier_register(struct ssam_controller *ctrl,
+			   struct ssam_event_notifier *n);
+
+int ssam_notifier_unregister(struct ssam_controller *ctrl,
+			     struct ssam_event_notifier *n);
+
+#endif /* _SURFACE_SAM_SSH_H */
diff --git a/drivers/platform/x86/surface_sam/surface_sam_ssh_trace.h b/drivers/platform/x86/surface_sam/surface_sam_ssh_trace.h
new file mode 100644
index 000000000000..8ea9a2fc99d7
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_ssh_trace.h
@@ -0,0 +1,587 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM surface_sam_ssh
+
+#if !defined(_SURFACE_SAM_SSH_TRACE_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _SURFACE_SAM_SSH_TRACE_H
+
+#include <linux/tracepoint.h>
+
+#include "surface_sam_ssh.h"
+
+
+TRACE_DEFINE_ENUM(SSH_FRAME_TYPE_DATA_SEQ);
+TRACE_DEFINE_ENUM(SSH_FRAME_TYPE_DATA_NSQ);
+TRACE_DEFINE_ENUM(SSH_FRAME_TYPE_ACK);
+TRACE_DEFINE_ENUM(SSH_FRAME_TYPE_NAK);
+
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_LOCKED_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_QUEUED_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_PENDING_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_TRANSMITTING_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_TRANSMITTED_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_ACKED_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_CANCELED_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_COMPLETED_BIT);
+
+TRACE_DEFINE_ENUM(SSH_PACKET_TY_FLUSH_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_TY_SEQUENCED_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_TY_BLOCKING_BIT);
+
+TRACE_DEFINE_ENUM(SSH_PACKET_FLAGS_SF_MASK);
+TRACE_DEFINE_ENUM(SSH_PACKET_FLAGS_TY_MASK);
+
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_LOCKED_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_QUEUED_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_PENDING_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_TRANSMITTING_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_TRANSMITTED_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_RSPRCVD_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_CANCELED_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_COMPLETED_BIT);
+
+TRACE_DEFINE_ENUM(SSH_REQUEST_TY_FLUSH_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_TY_HAS_RESPONSE_BIT);
+
+TRACE_DEFINE_ENUM(SSH_REQUEST_FLAGS_SF_MASK);
+TRACE_DEFINE_ENUM(SSH_REQUEST_FLAGS_TY_MASK);
+
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SAM);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_BAT);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_TMP);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_PMC);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_FAN);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_PoM);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_DBG);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_KBD);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_FWU);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_UNI);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_LPC);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_TCL);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SFL);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_KIP);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_EXT);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_BLD);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_BAS);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SEN);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SRQ);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_MCU);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_HID);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_TCH);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_BKL);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_TAM);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_ACC);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_UFI);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_USC);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_PEN);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_VID);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_AUD);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SMC);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_KPD);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_REG);
+
+
+#define SSAM_PTR_UID_LEN		9
+#define SSAM_U8_FIELD_NOT_APPLICABLE	((u16)-1)
+#define SSAM_SEQ_NOT_APPLICABLE		((u16)-1)
+#define SSAM_RQID_NOT_APPLICABLE	((u32)-1)
+#define SSAM_SSH_TC_NOT_APPLICABLE	0
+
+
+#ifndef _SURFACE_SAM_SSH_TRACE_HELPERS
+#define _SURFACE_SAM_SSH_TRACE_HELPERS
+
+static inline void ssam_trace_ptr_uid(const void *ptr, char* uid_str)
+{
+	char buf[2 * sizeof(void*) + 1];
+
+	snprintf(buf, ARRAY_SIZE(buf), "%p", ptr);
+	memcpy(uid_str, &buf[ARRAY_SIZE(buf) - SSAM_PTR_UID_LEN],
+	       SSAM_PTR_UID_LEN);
+}
+
+static inline u16 ssam_trace_get_packet_seq(const struct ssh_packet *p)
+{
+	if (!p->data.ptr || p->data.len < SSH_MESSAGE_LENGTH(0))
+		return SSAM_SEQ_NOT_APPLICABLE;
+
+	return p->data.ptr[SSH_MSGOFFSET_FRAME(seq)];
+}
+
+static inline u32 ssam_trace_get_request_id(const struct ssh_packet *p)
+{
+	if (!p->data.ptr || p->data.len < SSH_COMMAND_MESSAGE_LENGTH(0))
+		return SSAM_RQID_NOT_APPLICABLE;
+
+	return get_unaligned_le16(&p->data.ptr[SSH_MSGOFFSET_COMMAND(rqid)]);
+}
+
+static inline u32 ssam_trace_get_request_tc(const struct ssh_packet *p)
+{
+	if (!p->data.ptr || p->data.len < SSH_COMMAND_MESSAGE_LENGTH(0))
+		return SSAM_SSH_TC_NOT_APPLICABLE;
+
+	return get_unaligned_le16(&p->data.ptr[SSH_MSGOFFSET_COMMAND(tc)]);
+}
+
+#endif /* _SURFACE_SAM_SSH_TRACE_HELPERS */
+
+#define ssam_trace_get_command_field_u8(packet, field) \
+	((!packet || packet->data.len < SSH_COMMAND_MESSAGE_LENGTH(0)) \
+	 ? 0 : p->data.ptr[SSH_MSGOFFSET_COMMAND(field)])
+
+#define ssam_show_generic_u8_field(value)				\
+	__print_symbolic(value,						\
+		{ SSAM_U8_FIELD_NOT_APPLICABLE, 	"N/A" }		\
+	)
+
+
+#define ssam_show_frame_type(ty)					\
+	__print_symbolic(ty,						\
+		{ SSH_FRAME_TYPE_DATA_SEQ, 		"DSEQ" },	\
+		{ SSH_FRAME_TYPE_DATA_NSQ, 		"DNSQ" },	\
+		{ SSH_FRAME_TYPE_ACK, 			"ACK"  },	\
+		{ SSH_FRAME_TYPE_NAK, 			"NAK"  }	\
+	)
+
+#define ssam_show_packet_type(type)					\
+	__print_flags(flags & SSH_PACKET_FLAGS_TY_MASK, "",		\
+		{ BIT(SSH_PACKET_TY_FLUSH_BIT),		"F" },		\
+		{ BIT(SSH_PACKET_TY_SEQUENCED_BIT),	"S" },		\
+		{ BIT(SSH_PACKET_TY_BLOCKING_BIT),	"B" }		\
+	)
+
+#define ssam_show_packet_state(state)					\
+	__print_flags(flags & SSH_PACKET_FLAGS_SF_MASK, "",		\
+		{ BIT(SSH_PACKET_SF_LOCKED_BIT), 	"L" },		\
+		{ BIT(SSH_PACKET_SF_QUEUED_BIT), 	"Q" },		\
+		{ BIT(SSH_PACKET_SF_PENDING_BIT), 	"P" },		\
+		{ BIT(SSH_PACKET_SF_TRANSMITTING_BIT), 	"S" },		\
+		{ BIT(SSH_PACKET_SF_TRANSMITTED_BIT), 	"T" },		\
+		{ BIT(SSH_PACKET_SF_ACKED_BIT), 	"A" },		\
+		{ BIT(SSH_PACKET_SF_CANCELED_BIT), 	"C" },		\
+		{ BIT(SSH_PACKET_SF_COMPLETED_BIT), 	"F" }		\
+	)
+
+#define ssam_show_packet_seq(seq)					\
+	__print_symbolic(seq,						\
+		{ SSAM_SEQ_NOT_APPLICABLE, 		"N/A" }		\
+	)
+
+
+#define ssam_show_request_type(flags)					\
+	__print_flags(flags & SSH_REQUEST_FLAGS_TY_MASK, "",		\
+		{ BIT(SSH_REQUEST_TY_FLUSH_BIT),	"F" },		\
+		{ BIT(SSH_REQUEST_TY_HAS_RESPONSE_BIT),	"R" }		\
+	)
+
+#define ssam_show_request_state(flags)					\
+	__print_flags(flags & SSH_REQUEST_FLAGS_SF_MASK, "",		\
+		{ BIT(SSH_REQUEST_SF_LOCKED_BIT), 	"L" },		\
+		{ BIT(SSH_REQUEST_SF_QUEUED_BIT), 	"Q" },		\
+		{ BIT(SSH_REQUEST_SF_PENDING_BIT), 	"P" },		\
+		{ BIT(SSH_REQUEST_SF_TRANSMITTING_BIT),	"S" },		\
+		{ BIT(SSH_REQUEST_SF_TRANSMITTED_BIT), 	"T" },		\
+		{ BIT(SSH_REQUEST_SF_RSPRCVD_BIT), 	"A" },		\
+		{ BIT(SSH_REQUEST_SF_CANCELED_BIT), 	"C" },		\
+		{ BIT(SSH_REQUEST_SF_COMPLETED_BIT), 	"F" }		\
+	)
+
+#define ssam_show_request_id(rqid)					\
+	__print_symbolic(rqid,						\
+		{ SSAM_RQID_NOT_APPLICABLE, 		"N/A" }		\
+	)
+
+#define ssam_show_ssh_tc(rqid)						\
+	__print_symbolic(rqid,						\
+		{ SSAM_SSH_TC_NOT_APPLICABLE, 		"N/A" },	\
+		{ SSAM_SSH_TC_SAM, 			"SAM" },	\
+		{ SSAM_SSH_TC_BAT, 			"BAT" },	\
+		{ SSAM_SSH_TC_TMP, 			"TMP" },	\
+		{ SSAM_SSH_TC_PMC, 			"PMC" },	\
+		{ SSAM_SSH_TC_FAN, 			"FAN" },	\
+		{ SSAM_SSH_TC_PoM, 			"PoM" },	\
+		{ SSAM_SSH_TC_DBG, 			"DBG" },	\
+		{ SSAM_SSH_TC_KBD, 			"KBD" },	\
+		{ SSAM_SSH_TC_FWU, 			"FWU" },	\
+		{ SSAM_SSH_TC_UNI, 			"UNI" },	\
+		{ SSAM_SSH_TC_LPC, 			"LPC" },	\
+		{ SSAM_SSH_TC_TCL, 			"TCL" },	\
+		{ SSAM_SSH_TC_SFL, 			"SFL" },	\
+		{ SSAM_SSH_TC_KIP, 			"KIP" },	\
+		{ SSAM_SSH_TC_EXT, 			"EXT" },	\
+		{ SSAM_SSH_TC_BLD, 			"BLD" },	\
+		{ SSAM_SSH_TC_BAS, 			"BAS" },	\
+		{ SSAM_SSH_TC_SEN, 			"SEN" },	\
+		{ SSAM_SSH_TC_SRQ, 			"SRQ" },	\
+		{ SSAM_SSH_TC_MCU, 			"MCU" },	\
+		{ SSAM_SSH_TC_HID, 			"HID" },	\
+		{ SSAM_SSH_TC_TCH, 			"TCH" },	\
+		{ SSAM_SSH_TC_BKL, 			"BKL" },	\
+		{ SSAM_SSH_TC_TAM, 			"TAM" },	\
+		{ SSAM_SSH_TC_ACC, 			"ACC" },	\
+		{ SSAM_SSH_TC_UFI, 			"UFI" },	\
+		{ SSAM_SSH_TC_USC, 			"USC" },	\
+		{ SSAM_SSH_TC_PEN, 			"PEN" },	\
+		{ SSAM_SSH_TC_VID, 			"VID" },	\
+		{ SSAM_SSH_TC_AUD, 			"AUD" },	\
+		{ SSAM_SSH_TC_SMC, 			"SMC" },	\
+		{ SSAM_SSH_TC_KPD, 			"KPD" },	\
+		{ SSAM_SSH_TC_REG, 			"REG" }		\
+	)
+
+
+DECLARE_EVENT_CLASS(ssam_frame_class,
+	TP_PROTO(const struct ssh_frame *frame),
+
+	TP_ARGS(frame),
+
+	TP_STRUCT__entry(
+		__field(u8, type)
+		__field(u8, seq)
+		__field(u16, len)
+	),
+
+	TP_fast_assign(
+		__entry->type = frame->type;
+		__entry->seq = frame->seq;
+		__entry->len = get_unaligned_le16(&frame->len);
+	),
+
+	TP_printk("ty=%s, seq=0x%02x, len=%u",
+		ssam_show_frame_type(__entry->type),
+		__entry->seq,
+		__entry->len
+	)
+);
+
+#define DEFINE_SSAM_FRAME_EVENT(name)				\
+	DEFINE_EVENT(ssam_frame_class, ssam_##name,		\
+		TP_PROTO(const struct ssh_frame *frame),	\
+		TP_ARGS(frame)					\
+	)
+
+
+DECLARE_EVENT_CLASS(ssam_command_class,
+	TP_PROTO(const struct ssh_command *cmd, u16 len),
+
+	TP_ARGS(cmd, len),
+
+	TP_STRUCT__entry(
+		__field(u16, rqid)
+		__field(u16, len)
+		__field(u8, tc)
+		__field(u8, cid)
+		__field(u8, iid)
+	),
+
+	TP_fast_assign(
+		__entry->rqid = get_unaligned_le16(&cmd->rqid);
+		__entry->tc = cmd->tc;
+		__entry->cid = cmd->cid;
+		__entry->iid = cmd->iid;
+		__entry->len = len;
+	),
+
+	TP_printk("rqid=0x%04x, tc=%s, cid=0x%02x, iid=0x%02x, len=%u",
+		__entry->rqid,
+		ssam_show_ssh_tc(__entry->tc),
+		__entry->cid,
+		__entry->iid,
+		__entry->len
+	)
+);
+
+#define DEFINE_SSAM_COMMAND_EVENT(name)					\
+	DEFINE_EVENT(ssam_command_class, ssam_##name,			\
+		TP_PROTO(const struct ssh_command *cmd, u16 len),	\
+		TP_ARGS(cmd, len)					\
+	)
+
+
+DECLARE_EVENT_CLASS(ssam_packet_class,
+	TP_PROTO(const struct ssh_packet *packet),
+
+	TP_ARGS(packet),
+
+	TP_STRUCT__entry(
+		__array(char, uid, SSAM_PTR_UID_LEN)
+		__field(u8, priority)
+		__field(u16, length)
+		__field(unsigned long, state)
+		__field(u16, seq)
+	),
+
+	TP_fast_assign(
+		ssam_trace_ptr_uid(packet, __entry->uid);
+		__entry->priority = READ_ONCE(packet->priority);
+		__entry->length = packet->data.len;
+		__entry->state = READ_ONCE(packet->state);
+		__entry->seq = ssam_trace_get_packet_seq(packet);
+	),
+
+	TP_printk("uid=%s, seq=%s, ty=%s, pri=0x%02x, len=%u, sta=%s",
+		__entry->uid,
+		ssam_show_packet_seq(__entry->seq),
+		ssam_show_packet_type(__entry->state),
+		__entry->priority,
+		__entry->length,
+		ssam_show_packet_state(__entry->state)
+	)
+);
+
+#define DEFINE_SSAM_PACKET_EVENT(name)				\
+	DEFINE_EVENT(ssam_packet_class, ssam_##name,		\
+		TP_PROTO(const struct ssh_packet *packet),	\
+		TP_ARGS(packet)					\
+	)
+
+
+DECLARE_EVENT_CLASS(ssam_packet_status_class,
+	TP_PROTO(const struct ssh_packet *packet, int status),
+
+	TP_ARGS(packet, status),
+
+	TP_STRUCT__entry(
+		__array(char, uid, SSAM_PTR_UID_LEN)
+		__field(u8, priority)
+		__field(u16, length)
+		__field(unsigned long, state)
+		__field(u16, seq)
+		__field(int, status)
+	),
+
+	TP_fast_assign(
+		ssam_trace_ptr_uid(packet, __entry->uid);
+		__entry->priority = READ_ONCE(packet->priority);
+		__entry->length = packet->data.len;
+		__entry->state = READ_ONCE(packet->state);
+		__entry->seq = ssam_trace_get_packet_seq(packet);
+		__entry->status = status;
+	),
+
+	TP_printk("uid=%s, seq=%s, ty=%s, pri=0x%02x, len=%u, sta=%s, status=%d",
+		__entry->uid,
+		ssam_show_packet_seq(__entry->seq),
+		ssam_show_packet_type(__entry->state),
+		__entry->priority,
+		__entry->length,
+		ssam_show_packet_state(__entry->state),
+		__entry->status
+	)
+);
+
+#define DEFINE_SSAM_PACKET_STATUS_EVENT(name)				\
+	DEFINE_EVENT(ssam_packet_status_class, ssam_##name,		\
+		TP_PROTO(const struct ssh_packet *packet, int status),	\
+		TP_ARGS(packet, status)					\
+	)
+
+
+DECLARE_EVENT_CLASS(ssam_request_class,
+	TP_PROTO(const struct ssh_request *request),
+
+	TP_ARGS(request),
+
+	TP_STRUCT__entry(
+		__array(char, uid, SSAM_PTR_UID_LEN)
+		__field(unsigned long, state)
+		__field(u32, rqid)
+		__field(u8, tc)
+		__field(u16, cid)
+		__field(u16, iid)
+	),
+
+	TP_fast_assign(
+		const struct ssh_packet *p = &request->packet;
+
+		// use packet for UID so we can match requests to packets
+		ssam_trace_ptr_uid(p, __entry->uid);
+		__entry->state = READ_ONCE(request->state);
+		__entry->rqid = ssam_trace_get_request_id(p);
+		__entry->tc = ssam_trace_get_request_tc(p);
+		__entry->cid = ssam_trace_get_command_field_u8(p, cid);
+		__entry->iid = ssam_trace_get_command_field_u8(p, iid);
+	),
+
+	TP_printk("uid=%s, rqid=%s, ty=%s, sta=%s, tc=%s, cid=%s, iid=%s",
+		__entry->uid,
+		ssam_show_request_id(__entry->rqid),
+		ssam_show_request_type(__entry->state),
+		ssam_show_request_state(__entry->state),
+		ssam_show_ssh_tc(__entry->tc),
+		ssam_show_generic_u8_field(__entry->cid),
+		ssam_show_generic_u8_field(__entry->iid)
+	)
+);
+
+#define DEFINE_SSAM_REQUEST_EVENT(name)				\
+	DEFINE_EVENT(ssam_request_class, ssam_##name,		\
+		TP_PROTO(const struct ssh_request *request),	\
+		TP_ARGS(request)				\
+	)
+
+
+DECLARE_EVENT_CLASS(ssam_request_status_class,
+	TP_PROTO(const struct ssh_request *request, int status),
+
+	TP_ARGS(request, status),
+
+	TP_STRUCT__entry(
+		__array(char, uid, SSAM_PTR_UID_LEN)
+		__field(unsigned long, state)
+		__field(u32, rqid)
+		__field(u8, tc)
+		__field(u16, cid)
+		__field(u16, iid)
+		__field(int, status)
+	),
+
+	TP_fast_assign(
+		const struct ssh_packet *p = &request->packet;
+
+		// use packet for UID so we can match requests to packets
+		ssam_trace_ptr_uid(p, __entry->uid);
+		__entry->state = READ_ONCE(request->state);
+		__entry->rqid = ssam_trace_get_request_id(p);
+		__entry->tc = ssam_trace_get_request_tc(p);
+		__entry->cid = ssam_trace_get_command_field_u8(p, cid);
+		__entry->iid = ssam_trace_get_command_field_u8(p, iid);
+		__entry->status = status;
+	),
+
+	TP_printk("uid=%s, rqid=%s, ty=%s, sta=%s, tc=%s, cid=%s, iid=%s, status=%d",
+		__entry->uid,
+		ssam_show_request_id(__entry->rqid),
+		ssam_show_request_type(__entry->state),
+		ssam_show_request_state(__entry->state),
+		ssam_show_ssh_tc(__entry->tc),
+		ssam_show_generic_u8_field(__entry->cid),
+		ssam_show_generic_u8_field(__entry->iid),
+		__entry->status
+	)
+);
+
+#define DEFINE_SSAM_REQUEST_STATUS_EVENT(name)				\
+	DEFINE_EVENT(ssam_request_status_class, ssam_##name,		\
+		TP_PROTO(const struct ssh_request *request, int status),\
+		TP_ARGS(request, status)				\
+	)
+
+
+DECLARE_EVENT_CLASS(ssam_alloc_class,
+	TP_PROTO(void *ptr, size_t len),
+
+	TP_ARGS(ptr, len),
+
+	TP_STRUCT__entry(
+		__array(char, uid, SSAM_PTR_UID_LEN)
+		__field(size_t, len)
+	),
+
+	TP_fast_assign(
+		ssam_trace_ptr_uid(ptr, __entry->uid);
+		__entry->len = len;
+	),
+
+	TP_printk("uid=%s, len=%zu", __entry->uid, __entry->len)
+);
+
+#define DEFINE_SSAM_ALLOC_EVENT(name)					\
+	DEFINE_EVENT(ssam_alloc_class, ssam_##name,			\
+		TP_PROTO(void *ptr, size_t len),			\
+		TP_ARGS(ptr, len)					\
+	)
+
+
+DECLARE_EVENT_CLASS(ssam_free_class,
+	TP_PROTO(void *ptr),
+
+	TP_ARGS(ptr),
+
+	TP_STRUCT__entry(
+		__array(char, uid, SSAM_PTR_UID_LEN)
+		__field(size_t, len)
+	),
+
+	TP_fast_assign(
+		ssam_trace_ptr_uid(ptr, __entry->uid);
+	),
+
+	TP_printk("uid=%s", __entry->uid)
+);
+
+#define DEFINE_SSAM_FREE_EVENT(name)					\
+	DEFINE_EVENT(ssam_free_class, ssam_##name,			\
+		TP_PROTO(void *ptr),					\
+		TP_ARGS(ptr)						\
+	)
+
+
+DECLARE_EVENT_CLASS(ssam_generic_uint_class,
+	TP_PROTO(const char* property, unsigned int value),
+
+	TP_ARGS(property, value),
+
+	TP_STRUCT__entry(
+		__string(property, property)
+		__field(unsigned int, value)
+	),
+
+	TP_fast_assign(
+		__assign_str(property, property);
+		__entry->value = value;
+	),
+
+	TP_printk("%s=%u", __get_str(property), __entry->value)
+);
+
+#define DEFINE_SSAM_GENERIC_UINT_EVENT(name)				\
+	DEFINE_EVENT(ssam_generic_uint_class, ssam_##name,		\
+		TP_PROTO(const char* property, unsigned int value),	\
+		TP_ARGS(property, value)				\
+	)
+
+
+DEFINE_SSAM_FRAME_EVENT(rx_frame_received);
+DEFINE_SSAM_COMMAND_EVENT(rx_response_received);
+DEFINE_SSAM_COMMAND_EVENT(rx_event_received);
+
+DEFINE_SSAM_PACKET_EVENT(packet_release);
+DEFINE_SSAM_PACKET_EVENT(packet_submit);
+DEFINE_SSAM_PACKET_EVENT(packet_resubmit);
+DEFINE_SSAM_PACKET_EVENT(packet_timeout);
+DEFINE_SSAM_PACKET_EVENT(packet_cancel);
+DEFINE_SSAM_PACKET_STATUS_EVENT(packet_complete);
+DEFINE_SSAM_GENERIC_UINT_EVENT(ptl_timeout_reap);
+
+DEFINE_SSAM_REQUEST_EVENT(request_submit);
+DEFINE_SSAM_REQUEST_EVENT(request_timeout);
+DEFINE_SSAM_REQUEST_EVENT(request_cancel);
+DEFINE_SSAM_REQUEST_STATUS_EVENT(request_complete);
+DEFINE_SSAM_GENERIC_UINT_EVENT(rtl_timeout_reap);
+
+DEFINE_SSAM_PACKET_EVENT(ei_tx_drop_ack_packet);
+DEFINE_SSAM_PACKET_EVENT(ei_tx_drop_nak_packet);
+DEFINE_SSAM_PACKET_EVENT(ei_tx_drop_dsq_packet);
+DEFINE_SSAM_PACKET_STATUS_EVENT(ei_tx_fail_write);
+DEFINE_SSAM_PACKET_EVENT(ei_tx_corrupt_data);
+DEFINE_SSAM_GENERIC_UINT_EVENT(ei_rx_corrupt_syn);
+DEFINE_SSAM_FRAME_EVENT(ei_rx_corrupt_data);
+DEFINE_SSAM_REQUEST_EVENT(ei_rx_drop_response);
+
+DEFINE_SSAM_ALLOC_EVENT(ctrl_packet_alloc);
+DEFINE_SSAM_FREE_EVENT(ctrl_packet_free);
+
+DEFINE_SSAM_ALLOC_EVENT(event_item_alloc);
+DEFINE_SSAM_FREE_EVENT(event_item_free);
+
+#endif /* _SURFACE_SAM_SSH_TRACE_H */
+
+/* This part must be outside protection */
+#undef TRACE_INCLUDE_PATH
+#undef TRACE_INCLUDE_FILE
+
+#define TRACE_INCLUDE_PATH .
+#define TRACE_INCLUDE_FILE surface_sam_ssh_trace
+
+#include <trace/define_trace.h>
diff --git a/drivers/platform/x86/surface_sam/surface_sam_vhf.c b/drivers/platform/x86/surface_sam/surface_sam_vhf.c
new file mode 100644
index 000000000000..8455f952c272
--- /dev/null
+++ b/drivers/platform/x86/surface_sam/surface_sam_vhf.c
@@ -0,0 +1,266 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Virtual HID Framework (VHF) driver for input events via SAM.
+ * Used for keyboard input events on the Surface Laptops.
+ */
+
+#include <linux/acpi.h>
+#include <linux/hid.h>
+#include <linux/input.h>
+#include <linux/platform_device.h>
+#include <linux/types.h>
+
+#include "surface_sam_ssh.h"
+
+
+#define USB_VENDOR_ID_MICROSOFT		0x045e
+#define USB_DEVICE_ID_MS_VHF		0xf001
+
+#define VHF_INPUT_NAME			"Microsoft Virtual HID Framework Device"
+
+
+struct vhf_drvdata {
+	struct platform_device *dev;
+	struct ssam_controller *ctrl;
+
+	struct ssam_event_notifier notif;
+
+	struct hid_device *hid;
+};
+
+
+/*
+ * These report descriptors have been extracted from a Surface Book 2.
+ * They seems to be similar enough to be usable on the Surface Laptop.
+ */
+static const u8 vhf_hid_desc[] = {
+	// keyboard descriptor (event command ID 0x03)
+	0x05, 0x01,             /*  Usage Page (Desktop),                   */
+	0x09, 0x06,             /*  Usage (Keyboard),                       */
+	0xA1, 0x01,             /*  Collection (Application),               */
+	0x85, 0x01,             /*      Report ID (1),                      */
+	0x15, 0x00,             /*      Logical Minimum (0),                */
+	0x25, 0x01,             /*      Logical Maximum (1),                */
+	0x75, 0x01,             /*      Report Size (1),                    */
+	0x95, 0x08,             /*      Report Count (8),                   */
+	0x05, 0x07,             /*      Usage Page (Keyboard),              */
+	0x19, 0xE0,             /*      Usage Minimum (KB Leftcontrol),     */
+	0x29, 0xE7,             /*      Usage Maximum (KB Right GUI),       */
+	0x81, 0x02,             /*      Input (Variable),                   */
+	0x75, 0x08,             /*      Report Size (8),                    */
+	0x95, 0x0A,             /*      Report Count (10),                  */
+	0x19, 0x00,             /*      Usage Minimum (None),               */
+	0x29, 0x91,             /*      Usage Maximum (KB LANG2),           */
+	0x26, 0xFF, 0x00,       /*      Logical Maximum (255),              */
+	0x81, 0x00,             /*      Input,                              */
+	0x05, 0x0C,             /*      Usage Page (Consumer),              */
+	0x0A, 0xC0, 0x02,       /*      Usage (02C0h),                      */
+	0xA1, 0x02,             /*      Collection (Logical),               */
+	0x1A, 0xC1, 0x02,       /*          Usage Minimum (02C1h),          */
+	0x2A, 0xC6, 0x02,       /*          Usage Maximum (02C6h),          */
+	0x95, 0x06,             /*          Report Count (6),               */
+	0xB1, 0x03,             /*          Feature (Constant, Variable),   */
+	0xC0,                   /*      End Collection,                     */
+	0x05, 0x08,             /*      Usage Page (LED),                   */
+	0x19, 0x01,             /*      Usage Minimum (01h),                */
+	0x29, 0x03,             /*      Usage Maximum (03h),                */
+	0x75, 0x01,             /*      Report Size (1),                    */
+	0x95, 0x03,             /*      Report Count (3),                   */
+	0x25, 0x01,             /*      Logical Maximum (1),                */
+	0x91, 0x02,             /*      Output (Variable),                  */
+	0x95, 0x05,             /*      Report Count (5),                   */
+	0x91, 0x01,             /*      Output (Constant),                  */
+	0xC0,                   /*  End Collection,                         */
+
+	// media key descriptor (event command ID 0x04)
+	0x05, 0x0C,             /*  Usage Page (Consumer),                  */
+	0x09, 0x01,             /*  Usage (Consumer Control),               */
+	0xA1, 0x01,             /*  Collection (Application),               */
+	0x85, 0x03,             /*      Report ID (3),                      */
+	0x75, 0x10,             /*      Report Size (16),                   */
+	0x15, 0x00,             /*      Logical Minimum (0),                */
+	0x26, 0xFF, 0x03,       /*      Logical Maximum (1023),             */
+	0x19, 0x00,             /*      Usage Minimum (00h),                */
+	0x2A, 0xFF, 0x03,       /*      Usage Maximum (03FFh),              */
+	0x81, 0x00,             /*      Input,                              */
+	0xC0,                   /*  End Collection,                         */
+};
+
+
+static int vhf_hid_start(struct hid_device *hid)
+{
+	hid_dbg(hid, "%s\n", __func__);
+	return 0;
+}
+
+static void vhf_hid_stop(struct hid_device *hid)
+{
+	hid_dbg(hid, "%s\n", __func__);
+}
+
+static int vhf_hid_open(struct hid_device *hid)
+{
+	hid_dbg(hid, "%s\n", __func__);
+	return 0;
+}
+
+static void vhf_hid_close(struct hid_device *hid)
+{
+	hid_dbg(hid, "%s\n", __func__);
+}
+
+static int vhf_hid_parse(struct hid_device *hid)
+{
+	return hid_parse_report(hid, (u8 *)vhf_hid_desc, ARRAY_SIZE(vhf_hid_desc));
+}
+
+static int vhf_hid_raw_request(struct hid_device *hid, unsigned char reportnum,
+			       u8 *buf, size_t len, unsigned char rtype,
+			       int reqtype)
+{
+	hid_dbg(hid, "%s\n", __func__);
+	return 0;
+}
+
+static int vhf_hid_output_report(struct hid_device *hid, u8 *buf, size_t len)
+{
+	hid_dbg(hid, "%s\n", __func__);
+	print_hex_dump_debug("report:", DUMP_PREFIX_OFFSET, 16, 1, buf, len, false);
+
+	return len;
+}
+
+static struct hid_ll_driver vhf_hid_ll_driver = {
+	.start         = vhf_hid_start,
+	.stop          = vhf_hid_stop,
+	.open          = vhf_hid_open,
+	.close         = vhf_hid_close,
+	.parse         = vhf_hid_parse,
+	.raw_request   = vhf_hid_raw_request,
+	.output_report = vhf_hid_output_report,
+};
+
+
+static struct hid_device *vhf_create_hid_device(struct platform_device *pdev)
+{
+	struct hid_device *hid;
+
+	hid = hid_allocate_device();
+	if (IS_ERR(hid))
+		return hid;
+
+	hid->dev.parent = &pdev->dev;
+
+	hid->bus     = BUS_VIRTUAL;
+	hid->vendor  = USB_VENDOR_ID_MICROSOFT;
+	hid->product = USB_DEVICE_ID_MS_VHF;
+
+	hid->ll_driver = &vhf_hid_ll_driver;
+
+	sprintf(hid->name, "%s", VHF_INPUT_NAME);
+
+	return hid;
+}
+
+static u32 vhf_event_handler(struct ssam_notifier_block *nb, const struct ssam_event *event)
+{
+	struct vhf_drvdata *drvdata = container_of(nb, struct vhf_drvdata, notif.base);
+	int status;
+
+	if (event->target_category != 0x08)
+		return 0;
+
+	if (event->command_id == 0x03 || event->command_id == 0x04) {
+		status = hid_input_report(drvdata->hid, HID_INPUT_REPORT, (u8 *)&event->data[0], event->length, 1);
+		return ssam_notifier_from_errno(status) | SSAM_NOTIF_HANDLED;
+	}
+
+	return 0;
+}
+
+static int surface_sam_vhf_probe(struct platform_device *pdev)
+{
+	struct ssam_controller *ctrl;
+	struct vhf_drvdata *drvdata;
+	struct hid_device *hid;
+	int status;
+
+	// add device link to EC
+	status = ssam_client_bind(&pdev->dev, &ctrl);
+	if (status)
+		return status == -ENXIO ? -EPROBE_DEFER : status;
+
+	drvdata = kzalloc(sizeof(struct vhf_drvdata), GFP_KERNEL);
+	if (!drvdata)
+		return -ENOMEM;
+
+	hid = vhf_create_hid_device(pdev);
+	if (IS_ERR(hid)) {
+		status = PTR_ERR(hid);
+		goto err_probe_hid;
+	}
+
+	status = hid_add_device(hid);
+	if (status)
+		goto err_add_hid;
+
+	drvdata->dev = pdev;
+	drvdata->ctrl = ctrl;
+	drvdata->hid = hid;
+
+	drvdata->notif.base.priority = 1;
+	drvdata->notif.base.fn = vhf_event_handler;
+	drvdata->notif.event.reg = SSAM_EVENT_REGISTRY_SAM;
+	drvdata->notif.event.id.target_category = SSAM_SSH_TC_KBD;
+	drvdata->notif.event.id.instance = 0;
+	drvdata->notif.event.flags = 0;
+
+	platform_set_drvdata(pdev, drvdata);
+
+	status = ssam_notifier_register(ctrl, &drvdata->notif);
+	if (status)
+		goto err_add_hid;
+
+	return 0;
+
+err_add_hid:
+	hid_destroy_device(hid);
+	platform_set_drvdata(pdev, NULL);
+err_probe_hid:
+	kfree(drvdata);
+	return status;
+}
+
+static int surface_sam_vhf_remove(struct platform_device *pdev)
+{
+	struct vhf_drvdata *drvdata = platform_get_drvdata(pdev);
+
+	ssam_notifier_unregister(drvdata->ctrl, &drvdata->notif);
+	hid_destroy_device(drvdata->hid);
+	kfree(drvdata);
+
+	platform_set_drvdata(pdev, NULL);
+	return 0;
+}
+
+
+static const struct acpi_device_id surface_sam_vhf_match[] = {
+	{ "MSHW0096" },
+	{ },
+};
+MODULE_DEVICE_TABLE(acpi, surface_sam_vhf_match);
+
+static struct platform_driver surface_sam_vhf = {
+	.probe = surface_sam_vhf_probe,
+	.remove = surface_sam_vhf_remove,
+	.driver = {
+		.name = "surface_sam_vhf",
+		.acpi_match_table = surface_sam_vhf_match,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+module_platform_driver(surface_sam_vhf);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("Virtual HID Framework Driver for 5th Generation Surface Devices");
+MODULE_LICENSE("GPL");
-- 
2.26.2