IOS: Simplify IPC initialisation

The extra IPC ack is triggered by a syscall that is invoked in ES's
main function; the syscall literally just sets Y2, IX1 and IX2 in
HW_IPC_ARMCTRL -- there is no complicated ack queue or anything.

Source/Core/Core/IOS/ES/ES.cpp

@@ -122,6 +122,8 @@ void ESDevice::FinalizeEmulationState()
 
 void ESDevice::FinishInit()
 {
+  m_ios.InitIPC();
+
   if (s_title_to_launch != 0)
   {
     NOTICE_LOG_FMT(IOS, "Re-launching title after IOS reload.");

Source/Core/Core/IOS/IOS.cpp

@@ -64,7 +64,6 @@ namespace IOS::HLE
 static std::unique_ptr<EmulationKernel> s_ios;
 
 constexpr u64 ENQUEUE_REQUEST_FLAG = 0x100000000ULL;
-constexpr u64 ENQUEUE_ACKNOWLEDGEMENT_FLAG = 0x200000000ULL;
 static CoreTiming::EventType* s_event_enqueue;
 static CoreTiming::EventType* s_event_sdio_notify;
 static CoreTiming::EventType* s_event_finish_ppc_bootstrap;
@@ -289,9 +288,6 @@ EmulationKernel::EmulationKernel(u64 title_id) : Kernel(title_id)
     return;
   }
 
-  // IOS re-inits IPC and sends a dummy ack during its boot process.
-  EnqueueIPCAcknowledgement(0);
-
   AddCoreDevices();
   AddStaticDevices();
 }
@@ -443,6 +439,15 @@ bool Kernel::BootIOS(const u64 ios_title_id, const std::string& boot_content_pat
   return true;
 }
 
+void Kernel::InitIPC()
+{
+  if (s_ios == nullptr)
+    return;
+
+  INFO_LOG_FMT(IOS, "IPC initialised.");
+  GenerateAck(0);
+}
+
 void Kernel::AddDevice(std::unique_ptr<Device> device)
 {
   ASSERT(device->GetDeviceType() == Device::DeviceType::Static);
@@ -690,17 +695,9 @@ void Kernel::EnqueueIPCReply(const Request& request, const s32 return_value, s64
   CoreTiming::ScheduleEvent(cycles_in_future, s_event_enqueue, request.address, from);
 }
 
-void Kernel::EnqueueIPCAcknowledgement(u32 address, int cycles_in_future)
-{
-  CoreTiming::ScheduleEvent(cycles_in_future, s_event_enqueue,
-                            address | ENQUEUE_ACKNOWLEDGEMENT_FLAG);
-}
-
 void Kernel::HandleIPCEvent(u64 userdata)
 {
-  if (userdata & ENQUEUE_ACKNOWLEDGEMENT_FLAG)
+  if (userdata & ENQUEUE_REQUEST_FLAG)
-    m_ack_queue.push_back(static_cast<u32>(userdata));
-  else if (userdata & ENQUEUE_REQUEST_FLAG)
     m_request_queue.push_back(static_cast<u32>(userdata));
   else
     m_reply_queue.push_back(static_cast<u32>(userdata));
@@ -730,14 +727,6 @@ void Kernel::UpdateIPC()
     m_reply_queue.pop_front();
     return;
   }
-
-  if (!m_ack_queue.empty())
-  {
-    GenerateAck(m_ack_queue.front());
-    WARN_LOG_FMT(IOS, "<<-- Double-ack to IPC Request @ {:#010x}", m_ack_queue.front());
-    m_ack_queue.pop_front();
-    return;
-  }
 }
 
 void Kernel::UpdateDevices()

Source/Core/Core/IOS/IOS.h

@@ -133,6 +133,7 @@ public:
 
   bool BootstrapPPC(const std::string& boot_content_path);
   bool BootIOS(u64 ios_title_id, const std::string& boot_content_path = "");
+  void InitIPC();
   u32 GetVersion() const;
 
   IOSC& GetIOSC();
@@ -142,7 +143,6 @@ protected:
 
   void ExecuteIPCCommand(u32 address);
   std::optional<IPCReply> HandleIPCCommand(const Request& request);
-  void EnqueueIPCAcknowledgement(u32 address, int cycles_in_future = 0);
 
   void AddDevice(std::unique_ptr<Device> device);
   void AddCoreDevices();
@@ -165,7 +165,6 @@ protected:
   using IPCMsgQueue = std::deque<u32>;
   IPCMsgQueue m_request_queue;  // ppc -> arm
   IPCMsgQueue m_reply_queue;    // arm -> ppc
-  IPCMsgQueue m_ack_queue;      // arm -> ppc
   u64 m_last_reply_time = 0;
 
   IOSC m_iosc;