dma_pusher: Rework command_headers usage

Uses ScratchBuffer and avoids overwriting the command_headers buffer with the prefetch_command_list

src/video_core/dma_pusher.cpp

@@ -56,7 +56,7 @@ bool DmaPusher::Step() {
 
     if (command_list.prefetch_command_list.size()) {
         // Prefetched command list from nvdrv, used for things like synchronization
-        command_headers = std::move(command_list.prefetch_command_list);
+        ProcessCommands(command_list.prefetch_command_list);
         dma_pushbuffer.pop();
     } else {
         const CommandListHeader command_list_header{
@@ -82,16 +82,21 @@ bool DmaPusher::Step() {
             memory_manager.ReadBlockUnsafe(dma_get, command_headers.data(),
                                            command_list_header.size * sizeof(u32));
         }
+        ProcessCommands(command_headers);
     }
-    for (std::size_t index = 0; index < command_headers.size();) {
-        const CommandHeader& command_header = command_headers[index];
+
+    return true;
+}
+
+void DmaPusher::ProcessCommands(std::span<const CommandHeader> commands) {
+    for (std::size_t index = 0; index < commands.size();) {
+        const CommandHeader& command_header = commands[index];
 
         if (dma_state.method_count) {
             // Data word of methods command
             if (dma_state.non_incrementing) {
                 const u32 max_write = static_cast<u32>(
-                    std::min<std::size_t>(index + dma_state.method_count, command_headers.size()) -
-                    index);
+                    std::min<std::size_t>(index + dma_state.method_count, commands.size()) - index);
                 CallMultiMethod(&command_header.argument, max_write);
                 dma_state.method_count -= max_write;
                 dma_state.is_last_call = true;
@@ -142,8 +147,6 @@ bool DmaPusher::Step() {
         }
         index++;
     }
-
-    return true;
 }
 
 void DmaPusher::SetState(const CommandHeader& command_header) {

src/video_core/dma_pusher.h

@@ -4,11 +4,13 @@
 #pragma once
 
 #include <array>
+#include <span>
 #include <vector>
 #include <queue>
 
 #include "common/bit_field.h"
 #include "common/common_types.h"
+#include "common/scratch_buffer.h"
 #include "video_core/engines/engine_interface.h"
 #include "video_core/engines/puller.h"
 
@@ -136,13 +138,15 @@ private:
     static constexpr u32 non_puller_methods = 0x40;
     static constexpr u32 max_subchannels = 8;
     bool Step();
+    void ProcessCommands(std::span<const CommandHeader> commands);
 
     void SetState(const CommandHeader& command_header);
 
     void CallMethod(u32 argument) const;
     void CallMultiMethod(const u32* base_start, u32 num_methods) const;
 
-    std::vector<CommandHeader> command_headers; ///< Buffer for list of commands fetched at once
+    Common::ScratchBuffer<CommandHeader>
+        command_headers; ///< Buffer for list of commands fetched at once
 
     std::queue<CommandList> dma_pushbuffer; ///< Queue of command lists to be processed
     std::size_t dma_pushbuffer_subindex{};  ///< Index within a command list within the pushbuffer
@@ -159,7 +163,7 @@ private:
     DmaState dma_state{};
     bool dma_increment_once{};
 
-    bool ib_enable{true}; ///< IB mode enabled
+    const bool ib_enable{true}; ///< IB mode enabled
 
     std::array<Engines::EngineInterface*, max_subchannels> subchannels{};