On 2020-11-13 12:45, Daniel Vetter wrote:
On Thu, Nov 12, 2020 at 10:27:23AM -0800, Veera Sundaram Sankaran
wrote:
The explicit out-fences in crtc are signaled as part of vblank event,
indicating all framebuffers present on the Atomic Commit request are
scanned out on the screen. Though the fence signal and the vblank
event
notification happens at the same time, triggered by the same hardware
vsync event, the timestamp set in both are different. With drivers
supporting precise vblank timestamp the difference between the two
timestamps would be even higher. This might have an impact on use-mode
frameworks using these fence timestamps for purposes other than simple
buffer usage. For instance, the Android framework uses the
retire-fences
as an alternative to vblank when frame-updates are in progress Set the
fence timestamp during send vblank event to avoid discrepancies.
I think a reference to the exact source code in android that does this
would be really useful. Something in drm_hwcomposer or whatever is
doing
this.
Thanks for the review. Sorry for not getting back earlier, was waiting
for the review on [patch 1/2], so that both comments can be addressed
together.
Here is the reference for Android expecting retire-fence timestamp to
match exactly with hardware vsync as it is used for the dispsync model.
Usage: https://source.android.com/devices/graphics/implement-vsync
Code:
https://android.googlesource.com/platform/frameworks/native/+/master/services/surfaceflinger/Scheduler/Scheduler.cpp#397
Will update the commit-text with the links as part of V2 patch.
Thanks,
Veera
Aside from documenting why we want to do this I think this all looks
reasonable.
-Daniel
Signed-off-by: Veera Sundaram Sankaran <veeras@xxxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_vblank.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/gpu/drm/drm_vblank.c
b/drivers/gpu/drm/drm_vblank.c
index b18e1ef..b38e50c 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -24,6 +24,7 @@
* OTHER DEALINGS IN THE SOFTWARE.
*/
+#include <linux/dma-fence.h>
#include <linux/export.h>
#include <linux/kthread.h>
#include <linux/moduleparam.h>
@@ -999,6 +1000,14 @@ static void send_vblank_event(struct drm_device
*dev,
e->event.seq.time_ns = ktime_to_ns(now);
break;
}
+
+ /*
+ * update fence timestamp with the same vblank timestamp as both
+ * are signaled by the same event
+ */
+ if (e->base.fence)
+ e->base.fence->timestamp = now;
+
trace_drm_vblank_event_delivered(e->base.file_priv, e->pipe, seq);
drm_send_event_locked(dev, &e->base);
}
--
2.7.4
