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-rw-r--r--include/drm/drm_vblank.h15
1 files changed, 13 insertions, 2 deletions
diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
index 9fe4ba8bc622..c16c44052b3d 100644
--- a/include/drm/drm_vblank.h
+++ b/include/drm/drm_vblank.h
@@ -109,9 +109,20 @@ struct drm_vblank_crtc {
seqlock_t seqlock;
/**
- * @count: Current software vblank counter.
+ * @count:
+ *
+ * Current software vblank counter.
+ *
+ * Note that for a given vblank counter value drm_crtc_handle_vblank()
+ * and drm_crtc_vblank_count() or drm_crtc_vblank_count_and_time()
+ * provide a barrier: Any writes done before calling
+ * drm_crtc_handle_vblank() will be visible to callers of the later
+ * functions, iff the vblank count is the same or a later one.
+ *
+ * IMPORTANT: This guarantee requires barriers, therefor never access
+ * this field directly. Use drm_crtc_vblank_count() instead.
*/
- u64 count;
+ atomic64_t count;
/**
* @time: Vblank timestamp corresponding to @count.
*/