EXI: Add method to disable writes in CEXIMemoryCard.

Source/Core/Core/HW/EXI/EXI_DeviceMemoryCard.cpp

@@ -180,6 +180,11 @@ s32 CEXIMemoryCard::ReadFromMemcard(u32 memcard_offset, s32 length, u8* dest_add
   return m_memory_card->Read(memcard_offset, length, dest_address);
 }
 
+void CEXIMemoryCard::DisableWrites()
+{
+  m_allow_writes = false;
+}
+
 void CEXIMemoryCard::SetupGciFolder(const Memcard::HeaderData& header_data)
 {
   const std::string& game_id = SConfig::GetInstance().GetGameID();
@@ -297,6 +302,7 @@ void CEXIMemoryCard::SetCS(int cs)
     case Command::SectorErase:
       if (m_position > 2)
       {
+        if (m_allow_writes)
           m_memory_card->ClearBlock(m_address & (m_memory_card_size - 1));
         m_status |= MC_STATUS_BUSY;
         m_status &= ~MC_STATUS_READY;
@@ -310,6 +316,7 @@ void CEXIMemoryCard::SetCS(int cs)
     case Command::ChipErase:
       if (m_position > 2)
       {
+        if (m_allow_writes)
           m_memory_card->ClearAll();
         m_status &= ~MC_STATUS_BUSY;
       }
@@ -324,6 +331,7 @@ void CEXIMemoryCard::SetCS(int cs)
 
         while (count--)
         {
+          if (m_allow_writes)
             m_memory_card->Write(m_address, 1, &(m_programming_buffer[i++]));
           i &= 127;
           m_address = (m_address & ~0x1FF) | ((m_address + 1) & 0x1FF);
@@ -549,13 +557,17 @@ void CEXIMemoryCard::DMARead(u32 addr, u32 size)
 // DMA write are preceded by all of the necessary setup via IMMWrite
 // write all at once instead of single byte at a time as done by IEXIDevice::DMAWrite
 void CEXIMemoryCard::DMAWrite(u32 addr, u32 size)
+{
+  if (m_allow_writes)
   {
     auto& memory = m_system.GetMemory();
     m_memory_card->Write(m_address, size, memory.GetPointerForRange(addr, size));
+  }
 
   if (((m_address + size) % Memcard::BLOCK_SIZE) == 0)
   {
-    INFO_LOG_FMT(EXPANSIONINTERFACE, "writing to block: {:x}", m_address / Memcard::BLOCK_SIZE);
+    INFO_LOG_FMT(EXPANSIONINTERFACE, "{}writing to block: {:x}", m_allow_writes ? "" : "fake ",
+                 m_address / Memcard::BLOCK_SIZE);
   }
 
   // Schedule transfer complete later based on write speed

Source/Core/Core/HW/EXI/EXI_DeviceMemoryCard.h

@@ -66,6 +66,13 @@ public:
 
   s32 ReadFromMemcard(u32 memcard_offset, s32 length, u8* dest_address) const;
 
+  // After this call all writes to the card are disabled.
+  // This is used to have a 'grace period' after loading a savestate where the emulated software
+  // still sees the memory card but can't write to it anymore.
+  // It is expected that this device is destroyed and possibly recreated soon (within a few emulated
+  // frames) after this method has been called.
+  void DisableWrites();
+
 private:
   void SetupGciFolder(const Memcard::HeaderData& header_data);
   void SetupRawMemcard(u16 size_mb);
@@ -121,6 +128,7 @@ private:
   unsigned int m_address;
   u32 m_memory_card_size;
   std::unique_ptr<MemoryCardBase> m_memory_card;
+  bool m_allow_writes = true;
 
 protected:
   void TransferByte(u8& byte) override;