From b21bb9b24145e3f6b66b0e59f0519584aa01a8ab Mon Sep 17 00:00:00 2001
From: stransky <stransky@redhat.com>
Date: Tue, 13 May 2025 08:26:16 +0000
Subject: [PATCH] Bug 1961723 [Linux] Add WaylandBufferDMABUFHolder class to
 cache wl_buffer and allow WaylandBufferDMABUF to set wl_buffer from external
 source r=emilio

If DMABufSurface are recycled we don't want to create/delete wl_buffer for recycled frames as it eats GPU/power resources.
Instead store wl_buffers for DMABuf surfaces and re-use them if possible.
The behaviour is inspired by MPV which does the same.

Differential Revision: https://phabricator.services.mozilla.com/D248224
---
 widget/gtk/WaylandBuffer.cpp | 57 ++++++++++++++++++++++++++++++++++--
 widget/gtk/WaylandBuffer.h   | 27 +++++++++++++++++
 2 files changed, 81 insertions(+), 3 deletions(-)

diff --git a/widget/gtk/WaylandBuffer.cpp b/widget/gtk/WaylandBuffer.cpp
index 2fe430280a39..e366a7f09429 100644
--- a/widget/gtk/WaylandBuffer.cpp
+++ b/widget/gtk/WaylandBuffer.cpp
@@ -123,9 +123,15 @@ void WaylandBuffer::DeleteWlBuffer() {
   if (!mWLBuffer) {
     return;
   }
-  LOGWAYLAND("WaylandBuffer::DeleteWlBuffer() [%p] wl_buffer [%p]\n",
-             (void*)this, mWLBuffer);
-  MozClearPointer(mWLBuffer, wl_buffer_destroy);
+  LOGWAYLAND("WaylandBuffer::DeleteWlBuffer() [%p] wl_buffer [%p] managed %d",
+             (void*)this, mWLBuffer, mManagingWLBuffer);
+  if (mManagingWLBuffer) {
+    MozClearPointer(mWLBuffer, wl_buffer_destroy);
+  } else {
+    // Remove reference to this WaylandBuffer
+    wl_proxy_set_user_data((wl_proxy*)mWLBuffer, nullptr);
+    mWLBuffer = nullptr;
+  }
 }
 
 void WaylandBuffer::ReturnBufferDetached(WaylandSurfaceLock& aSurfaceLock) {
@@ -137,6 +143,28 @@ void WaylandBuffer::ReturnBufferDetached(WaylandSurfaceLock& aSurfaceLock) {
   mAttachedToSurface = nullptr;
 }
 
+wl_buffer* WaylandBuffer::CreateAndTakeWLBuffer() {
+  LOGWAYLAND("WaylandBuffer::CreateAndTakeWLBuffer() [%p]", (void*)this);
+  MOZ_DIAGNOSTIC_ASSERT(!mAttachedToSurface);
+
+  if (!CreateWlBuffer()) {
+    return nullptr;
+  }
+  mManagingWLBuffer = false;
+  return mWLBuffer;
+}
+
+void WaylandBuffer::SetExternalWLBuffer(wl_buffer* aWLBuffer) {
+  LOGWAYLAND("WaylandBuffer::SetExternalWLBuffer() [%p] wl_buffer %p",
+             (void*)this, aWLBuffer);
+  MOZ_DIAGNOSTIC_ASSERT(!mAttachedToSurface);
+  MOZ_DIAGNOSTIC_ASSERT(!mWLBuffer);
+
+  mManagingWLBuffer = false;
+  mWLBuffer = aWLBuffer;
+  mWLBufferID = reinterpret_cast<uintptr_t>(mWLBuffer);
+}
+
 struct SurfaceAndBuffer {
   SurfaceAndBuffer(WaylandSurface* aSurface, WaylandBuffer* aBuffer)
       : mSurface(aSurface), mBuffer(aBuffer) {};
@@ -378,4 +406,27 @@ void WaylandBufferDMABUF::DumpToFile(const char* aHint) {
 }
 #endif
 
+WaylandBufferDMABUFHolder::WaylandBufferDMABUFHolder(DMABufSurface* aSurface,
+                                                     wl_buffer* aWLBuffer)
+    : mWLBuffer(aWLBuffer) {
+  mUID = aSurface->GetUID();
+  mPID = aSurface->GetPID();
+  LOGWAYLAND(
+      "WaylandBufferDMABUFHolder::WaylandBufferDMABUFHolder wl_buffer [%p] UID "
+      "%d PID %d",
+      mWLBuffer, mUID, mPID);
+}
+
+WaylandBufferDMABUFHolder::~WaylandBufferDMABUFHolder() {
+  LOGWAYLAND(
+      "WaylandBufferDMABUFHolder::~WaylandBufferDMABUFHolder wl_buffer [%p] "
+      "UID %d PID %d",
+      mWLBuffer, mUID, mPID);
+  MozClearPointer(mWLBuffer, wl_buffer_destroy);
+}
+
+bool WaylandBufferDMABUFHolder::Matches(DMABufSurface* aSurface) const {
+  return mUID == aSurface->GetUID() && mPID == aSurface->GetPID();
+}
+
 }  // namespace mozilla::widget
diff --git a/widget/gtk/WaylandBuffer.h b/widget/gtk/WaylandBuffer.h
index 3a11e52db1dd..afd3329c0269 100644
--- a/widget/gtk/WaylandBuffer.h
+++ b/widget/gtk/WaylandBuffer.h
@@ -85,6 +85,13 @@ class WaylandBuffer {
   virtual void DumpToFile(const char* aHint) = 0;
 #endif
 
+  // Create and move away wl_buffer and mark is as not managed.
+  // From this point wl_buffer is not owned by WaylandBuffer.
+  wl_buffer* CreateAndTakeWLBuffer();
+
+  // Set wl_buffer from external source (WaylandBufferDMABUFHolder).
+  void SetExternalWLBuffer(wl_buffer* aWLBuffer);
+
  protected:
   explicit WaylandBuffer(const LayoutDeviceIntSize& aSize);
   virtual ~WaylandBuffer() = default;
@@ -105,6 +112,11 @@ class WaylandBuffer {
   wl_buffer* mWLBuffer = nullptr;
   uintptr_t mWLBufferID = 0;
 
+  // Owns and manages WL buffer. If set to false, wl_buffer is managed by
+  // someone else (for instance WaylandBufferDMABUFHolder)
+  // and WaylandBuffer can't destroy it.
+  bool mManagingWLBuffer = true;
+
   // Wayland buffer is tied to WaylandSurface.
   // We keep reference to WaylandSurface until WaylandSurface returns the
   // buffer.
@@ -192,6 +204,21 @@ class WaylandBufferDMABUF final : public WaylandBuffer {
   RefPtr<DMABufSurface> mDMABufSurface;
 };
 
+class WaylandBufferDMABUFHolder final {
+ public:
+  bool Matches(DMABufSurface* aSurface) const;
+
+  wl_buffer* GetWLBuffer() { return mWLBuffer; }
+
+  WaylandBufferDMABUFHolder(DMABufSurface* aSurface, wl_buffer* aWLBuffer);
+  ~WaylandBufferDMABUFHolder();
+
+ private:
+  wl_buffer* mWLBuffer = nullptr;
+  uint32_t mUID = 0;
+  uint32_t mPID = 0;
+};
+
 }  // namespace mozilla::widget
 
 #endif  // _MOZILLA_WIDGET_GTK_WAYLAND_BUFFER_H