Fix the P6 scratch save in R2UR/MATCH/HFMA2.RELU; GPU memory dump tool

The colour cast on title 1 (magenta/cyan, then red/green, changing per
course) came from the sky/atmosphere volume shader (a pixel shader drawing
a 32^3 RGBA16F table slice by slice), which starts with an unguarded R2UR.
R2UR, MATCH and HFMA2.RELU use P6 as scratch and saved/restored it with the
uniform-guard mask, 1 << (6 - 7) for an unguarded instruction: undefined, in
practice bit 31, which shifted into the opcode bits and turned the save into
another instruction. They now always save and restore P6.

Debugging aids used to find it:
- EDEN_NX2_DUMP=<present>:<addr>:<size>,...: flush GPU memory ranges at a
  present (on the GPU thread) and save them next to the frame captures;
  nx2work/vol3d.py untiles Switch 2 3D textures from such dumps.
- GPU::RunOnGpuThread.
- Logs of Switch 2 3D images and descriptors.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/video_core/gpu.cpp b/src/video_core/gpu.cpp
index 2a61a66d82..6441b9511a 100644
--- a/src/video_core/gpu.cpp
+++ b/src/video_core/gpu.cpp
@@ -411,6 +411,10 @@ u64 GPU::RequestFlush(DAddr addr, std::size_t size) {
     });
 }
 
+u64 GPU::RunOnGpuThread(std::function<void()>&& action) {
+    return impl->RequestSyncOperation(std::move(action));
+}
+
 u64 GPU::CurrentSyncRequestFence() const {
     return impl->CurrentSyncRequestFence();
 }