Kernel: Add interrupt support to aarch64 RPi Timer driver

Since we can now build and use the IRQHandler class, we can implement
interrupt support for the Timer in the aarch64 build.

Kernel/Arch/aarch64/RPi/Timer.cpp

@@ -30,7 +30,8 @@ enum FlagBits {
 };
 
 Timer::Timer()
-    : m_registers(MMIO::the().peripheral<TimerRegisters>(0x3000))
+    : IRQHandler(1)
+    , m_registers(MMIO::the().peripheral<TimerRegisters>(0x3000))
 {
 }
 
@@ -51,6 +52,41 @@ u64 Timer::microseconds_since_boot()
     return (static_cast<u64>(high) << 32) | low;
 }
 
+bool Timer::handle_irq(RegisterState const&)
+{
+    dbgln("Timer fired: {} us", m_current_timer_value);
+
+    m_current_timer_value += m_interrupt_interval;
+    set_compare(TimerID::Timer1, m_current_timer_value);
+
+    clear_interrupt(TimerID::Timer1);
+    return true;
+};
+
+void Timer::enable_interrupt_mode()
+{
+    m_current_timer_value = microseconds_since_boot();
+    m_current_timer_value += m_interrupt_interval;
+    set_compare(TimerID::Timer1, m_current_timer_value);
+
+    enable_irq();
+}
+
+void Timer::set_interrupt_interval_usec(u32 interrupt_interval)
+{
+    m_interrupt_interval = interrupt_interval;
+}
+
+void Timer::clear_interrupt(TimerID id)
+{
+    m_registers->control_and_status = 1 << to_underlying(id);
+}
+
+void Timer::set_compare(TimerID id, u32 compare)
+{
+    m_registers->compare[to_underlying(id)] = compare;
+}
+
 class SetClockRateMboxMessage : Mailbox::Message {
 public:
     u32 clock_id;

Kernel/Arch/aarch64/RPi/Timer.h

@@ -7,18 +7,22 @@
 #pragma once
 
 #include <AK/Types.h>
+#include <Kernel/Interrupts/IRQHandler.h>
 
 namespace Kernel::RPi {
 
 struct TimerRegisters;
 
-class Timer {
+class Timer : public IRQHandler {
 public:
     Timer();
     static Timer& the();
 
     u64 microseconds_since_boot();
 
+    void set_interrupt_interval_usec(u32);
+    void enable_interrupt_mode();
+
     enum class ClockID {
         Reserved = 0,
         EMMC = 1,
@@ -39,7 +43,21 @@ public:
     static u32 set_clock_rate(ClockID, u32 rate_hz, bool skip_setting_turbo = true);
 
 private:
+    enum class TimerID : u32 {
+        Timer0 = 0,
+        Timer1 = 1,
+        Timer2 = 2,
+        Timer3 = 3,
+    };
+    void set_compare(TimerID, u32 compare);
+    void clear_interrupt(TimerID);
+
+    //^ IRQHandler
+    virtual bool handle_irq(RegisterState const&) override;
+
     TimerRegisters volatile* m_registers;
+    u32 m_interrupt_interval { 0 };
+    u32 m_current_timer_value { 0 };
 };
 
 }