HWComposer: update the hwc_layer::handle docs
Change-Id: I3c1211146b2e5f84546724c86f344bd2e63bd55c
diff --git a/include/hardware/hwcomposer.h b/include/hardware/hwcomposer.h
index b4a7a7a..f788e46 100644
--- a/include/hardware/hwcomposer.h
+++ b/include/hardware/hwcomposer.h
@@ -150,8 +150,12 @@
/* see hwc_layer_t::flags above */
uint32_t flags;
- /* handle of buffer to compose. this handle is guaranteed to have been
- * allocated with gralloc */
+ /* handle of buffer to compose. This handle is guaranteed to have been
+ * allocated from gralloc using the GRALLOC_USAGE_HW_COMPOSER usage flag. If
+ * the layer's handle is unchanged across two consecutive prepare calls and
+ * the HWC_GEOMETRY_CHANGED flag is not set for the second call then the
+ * HWComposer implementation may assume that the contents of the buffer have
+ * not changed. */
buffer_handle_t handle;
/* transformation to apply to the buffer during composition */