improve hwc VSYNC documentation
Change-Id: I5820d8fa183701ebbc0a825cf27bd0004b47d62e
diff --git a/include/hardware/hwcomposer.h b/include/hardware/hwcomposer.h
index 7f55784..827cea1 100644
--- a/include/hardware/hwcomposer.h
+++ b/include/hardware/hwcomposer.h
@@ -331,6 +331,11 @@
* ANDROID_URGENT_DISPLAY_PRIORITY with as little latency as possible,
* typically less than 0.5 ms.
*
+ * It is a (silent) error to have HWC_EVENT_VSYNC enabled when calling
+ * hwc_composer_device.set(..., 0, 0, 0) (screen off). The implementation
+ * can either stop or continue to process VSYNC events, but must not
+ * crash or cause other problems.
+ *
*/
void (*vsync)(struct hwc_procs* procs, int zero, int64_t timestamp);
} hwc_procs_t;