From 6c6cc910e641e861e7e90ff38bf6734d2690ffd7 Mon Sep 17 00:00:00 2001
From: Stenzek <stenzek@gmail.com>
Date: Thu, 19 Jun 2025 21:14:56 +1000
Subject: [PATCH] DMA: Invalidate code pages on CD-ROM DMA write

Avoids page faulting by invalidating the pages in advance.

Might help with frame time spikes on super low-spec devices.
---
 src/core/bus.cpp |  5 -----
 src/core/bus.h   |  7 +++++--
 src/core/dma.cpp | 10 ++++++++++
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/src/core/bus.cpp b/src/core/bus.cpp
index a5f326a61..7b38d011c 100644
--- a/src/core/bus.cpp
+++ b/src/core/bus.cpp
@@ -699,11 +699,6 @@ bool Bus::CanUseFastmemForAddress(VirtualMemoryAddress address)
   }
 }
 
-bool Bus::IsRAMCodePage(u32 index)
-{
-  return g_ram_code_bits[index];
-}
-
 void Bus::SetRAMCodePage(u32 index)
 {
   if (g_ram_code_bits[index])
diff --git a/src/core/bus.h b/src/core/bus.h
index 0c0e613e4..917849bbc 100644
--- a/src/core/bus.h
+++ b/src/core/bus.h
@@ -170,7 +170,10 @@ ALWAYS_INLINE static u32 GetRAMCodePageIndex(PhysicalMemoryAddress address)
 }
 
 /// Returns true if the specified page contains code.
-bool IsRAMCodePage(u32 index);
+ALWAYS_INLINE static bool IsRAMCodePage(u32 index)
+{
+  return g_ram_code_bits[index];
+}
 
 /// Flags a RAM region as code, so we know when to invalidate blocks.
 void SetRAMCodePage(u32 index);
@@ -188,7 +191,7 @@ bool IsCodePageAddress(PhysicalMemoryAddress address);
 bool HasCodePagesInRange(PhysicalMemoryAddress start_address, u32 size);
 
 /// Returns the number of cycles stolen by DMA RAM access.
-ALWAYS_INLINE TickCount GetDMARAMTickCount(u32 word_count)
+ALWAYS_INLINE static TickCount GetDMARAMTickCount(u32 word_count)
 {
   // DMA is using DRAM Hyper Page mode, allowing it to access DRAM rows at 1 clock cycle per word (effectively around
   // 17 clks per 16 words, due to required row address loading, probably plus some further minimal overload due to
diff --git a/src/core/dma.cpp b/src/core/dma.cpp
index 21e71758a..45f1d6b55 100644
--- a/src/core/dma.cpp
+++ b/src/core/dma.cpp
@@ -4,6 +4,7 @@
 #include "dma.h"
 #include "bus.h"
 #include "cdrom.h"
+#include "cpu_code_cache.h"
 #include "cpu_core.h"
 #include "gpu.h"
 #include "gpu_dump.h"
@@ -895,6 +896,15 @@ TickCount DMA::TransferDeviceToMemory(u32 address, u32 increment, u32 word_count
       s_state.transfer_buffer.resize(word_count);
     dest_pointer = s_state.transfer_buffer.data();
   }
+  else if constexpr (channel == Channel::CDROM)
+  {
+    const u32 end_page = (address + (increment * word_count) - 1) >> HOST_PAGE_SHIFT;
+    for (u32 page = address >> HOST_PAGE_SHIFT; page <= end_page; page++)
+    {
+      if (Bus::IsRAMCodePage(page))
+        CPU::CodeCache::InvalidateBlocksWithPageIndex(page);
+    }
+  }
 
   // Read from device.
   switch (channel)