Merge "Clarify FRONT_BUFFER requirements"
diff --git a/graphics/common/aidl/android/hardware/graphics/common/BufferUsage.aidl b/graphics/common/aidl/android/hardware/graphics/common/BufferUsage.aidl
index 4b5a306..60dfbfb 100644
--- a/graphics/common/aidl/android/hardware/graphics/common/BufferUsage.aidl
+++ b/graphics/common/aidl/android/hardware/graphics/common/BufferUsage.aidl
@@ -107,7 +107,24 @@
/* Bits 28-31 are reserved for vendor usage */
/**
- * Buffer is used for front-buffer rendering
+ * Buffer is used for front-buffer rendering.
+ *
+ * To satisfy an allocation with this usage, the resulting buffer
+ * must operate as equivalent to shared memory for all targets.
+ *
+ * For CPU_USAGE_* other than NEVER, this means the buffer must
+ * "lock in place". The buffers must be directly accessible via mapping.
+ *
+ * For GPU_RENDER_TARGET the buffer must behave equivalent to a
+ * single-buffered EGL surface. For example glFlush must perform
+ * a flush, same as if the default framebuffer was single-buffered.
+ *
+ * For COMPOSER_* the HWC must not perform any caching for this buffer
+ * when submitted for composition. HWCs do not need to do any form
+ * of auto-refresh, and they are allowed to cache composition results between
+ * presents from SF (such as for panel self-refresh), but for any given
+ * present the buffer must be composited from even if it otherwise appears
+ * to be the same as a previous composition.
*/
FRONT_BUFFER = 1L << 32,
