Clear HWC layer buffer slots by assiging a placeholder buffer
When buffers are discarded by SurfaceFlinger clients, the memory should
be free'd immediately. This includes clearing references to them from
within the implementation of Composer HAL, specifically in cache slots
associated with the layer.
Since there is no HAL API to clear the slot directly, prior to writing
any other buffer to the layer, we set the layer's buffer multiple times
to a placeholder buffer, using each of the slot numbers that need to be
cleared. This replaces the reference to the client-discarded buffer
inside Composer HAL with a reference to the placeholder buffer, causing
the reference count to drop, allowing the buffer memory to be freed.
Bug: 258196272
Test: atest OutputLayerUncacheBufferTest
Change-Id: Id85482e8859490566f0eedbd8d8729c47a7349fb
diff --git a/services/surfaceflinger/DisplayHardware/HidlComposerHal.h b/services/surfaceflinger/DisplayHardware/HidlComposerHal.h
index 3602bbb..dc115b2 100644
--- a/services/surfaceflinger/DisplayHardware/HidlComposerHal.h
+++ b/services/surfaceflinger/DisplayHardware/HidlComposerHal.h
@@ -248,6 +248,7 @@
/* see setClientTarget for the purpose of slot */
Error setLayerBuffer(Display display, Layer layer, uint32_t slot,
const sp<GraphicBuffer>& buffer, int acquireFence) override;
+ Error clearLayerBufferSlot(Display display, Layer layer, uint32_t slot) override;
Error setLayerSurfaceDamage(Display display, Layer layer,
const std::vector<IComposerClient::Rect>& damage) override;
Error setLayerBlendMode(Display display, Layer layer, IComposerClient::BlendMode mode) override;
@@ -362,6 +363,9 @@
sp<V2_3::IComposerClient> mClient_2_3;
sp<IComposerClient> mClient_2_4;
+ // Buffer slots for layers are cleared by setting the slot buffer to this buffer.
+ sp<GraphicBuffer> mClearSlotBuffer;
+
// 64KiB minus a small space for metadata such as read/write pointers
static constexpr size_t kWriterInitialSize = 64 * 1024 / sizeof(uint32_t) - 16;
// Max number of buffers that may be cached for a given layer