From 95797b05f1fcc53ad4c932ec171a46bdde4b08de Mon Sep 17 00:00:00 2001
From: Stenzek <stenzek@gmail.com>
Date: Fri, 7 Mar 2025 15:49:05 +1000
Subject: [PATCH] GPU: Force early run on GP0 FIFO overflow

And don't crash if a game spams GP0 writes and it overflows.
---
 src/core/gpu.cpp | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/core/gpu.cpp b/src/core/gpu.cpp
index 097cabae3..d8f84fa3d 100644
--- a/src/core/gpu.cpp
+++ b/src/core/gpu.cpp
@@ -531,6 +531,19 @@ void GPU::WriteRegister(u32 offset, u32 value)
       if (m_gpu_dump) [[unlikely]]
         m_gpu_dump->WriteGP0Packet(value);
 
+      // FIFO can be overflowed through direct GP0 writes if the command tick event hasn't run, because
+      // there's no backpressure applied to the CPU. Instead force the GPU to run and catch up.
+      if (m_fifo.GetSize() >= m_fifo_size) [[unlikely]]
+      {
+        s_command_tick_event.InvokeEarly();
+
+        if (m_fifo.GetSize() >= m_fifo.GetCapacity()) [[unlikely]]
+        {
+          WARNING_LOG("GPU FIFO overflow via GP0 write, size={}", m_fifo.GetSize());
+          return;
+        }
+      }
+
       m_fifo.Push(value);
       ExecuteCommands();
       return;