SVC: Implement svcInfo:IdleTickCount

Used by the Witcher 3

src/core/hle/kernel/k_scheduler.h

@@ -49,6 +49,11 @@ public:
     /// Gets the current running thread
     [[nodiscard]] KThread* GetCurrentThread() const;
 
+    /// Gets the idle thread
+    [[nodiscard]] KThread* GetIdleThread() const {
+        return idle_thread;
+    }
+
     /// Returns true if the scheduler is idle
     [[nodiscard]] bool IsIdle() const {
         return GetCurrentThread() == idle_thread;

src/core/hle/kernel/svc.cpp

@@ -886,7 +886,24 @@ static ResultCode GetInfo(Core::System& system, u64* result, u64 info_id, Handle
         *result = out_ticks;
         return ResultSuccess;
     }
+    case GetInfoType::IdleTickCount: {
+        if (handle == 0) {
+            LOG_ERROR(Kernel_SVC, "Thread handle does not exist, handle=0x{:08X}",
+                      static_cast<Handle>(handle));
+            return ResultInvalidHandle;
+        }
 
+        if (info_sub_id != 0xFFFFFFFFFFFFFFFF && info_sub_id != system.CurrentCoreIndex()) {
+            LOG_ERROR(Kernel_SVC, "Core is not the current core, got {}", info_sub_id);
+            return ResultInvalidCombination;
+        }
+
+        const auto& scheduler = *system.Kernel().CurrentScheduler();
+        const auto* const idle_thread = scheduler.GetIdleThread();
+
+        *result = idle_thread->GetCpuTime();
+        return ResultSuccess;
+    }
     default:
         LOG_ERROR(Kernel_SVC, "Unimplemented svcGetInfo id=0x{:016X}", info_id);
         return ResultInvalidEnumValue;