feat: further kernel power and power optimizations

kernel/src/Drivers/Input/InputEvents.cpp

@@ -0,0 +1,70 @@
+/*
+    * InputEvents.cpp
+    * Shared input activity event source
+    * Copyright (c) 2026 Daniel Hammer
+*/
+
+#include "InputEvents.hpp"
+#include <atomic>
+#include <Sched/Scheduler.hpp>
+#include <Timekeeping/ApicTimer.hpp>
+
+namespace Drivers::InputEvents {
+
+    static std::atomic<uint64_t> g_serial{1};
+    static uint8_t g_waitObject;
+
+    struct WaitContext {
+        uint64_t observedSerial;
+    };
+
+    static bool SerialStillObserved(void* rawContext) {
+        auto* context = static_cast<WaitContext*>(rawContext);
+        return context != nullptr &&
+               g_serial.load(std::memory_order_acquire) == context->observedSerial;
+    }
+
+    uint64_t GetSerial() {
+        return g_serial.load(std::memory_order_acquire);
+    }
+
+    void NotifyActivity() {
+        Timekeeping::NoteInteractiveActivity();
+        g_serial.fetch_add(1, std::memory_order_release);
+        Sched::WakeObjectWaiters(&g_waitObject);
+    }
+
+    uint64_t WaitForChange(uint64_t observedSerial, uint64_t timeoutMs) {
+        uint64_t current = GetSerial();
+        if (current != observedSerial || timeoutMs == 0) {
+            return current;
+        }
+
+        WaitContext context{observedSerial};
+        uint64_t start = Timekeeping::GetMilliseconds();
+
+        for (;;) {
+            current = GetSerial();
+            if (current != observedSerial) {
+                return current;
+            }
+
+            uint64_t waitMs = 0;
+            if (timeoutMs == UINT64_MAX) {
+                waitMs = 0;
+            } else {
+                uint64_t elapsed = Timekeeping::GetMilliseconds() - start;
+                if (elapsed >= timeoutMs) {
+                    return current;
+                }
+                waitMs = timeoutMs - elapsed;
+                if (waitMs == 0) {
+                    waitMs = 1;
+                }
+            }
+
+            Sched::BlockOnObjectIf(&g_waitObject, waitMs, SerialStillObserved, &context);
+        }
+    }
+
+}