Re: [PATCH v3 2/2] drm/drm_vblank: set the dma-fence timestamp during send_vblank_event

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On Wed, Jan 13, 2021 at 11:52 AM Veera Sundaram Sankaran
<veeras@xxxxxxxxxxxxxx> 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 [1] uses the
> retire-fences as an alternative to vblank when frame-updates are in
> progress. Set the fence timestamp during send vblank event using a new
> drm_send_event_timestamp_locked variant to avoid discrepancies.
>
> [1] https://android.googlesource.com/platform/frameworks/native/+/master/
> services/surfaceflinger/Scheduler/Scheduler.cpp#397
>
> Changes in v2:
> - Use drm_send_event_timestamp_locked to update fence timestamp
> - add more information to commit text
>
> Changes in v3:
> - use same backend helper function for variants of drm_send_event to
> avoid code duplications
>
> Signed-off-by: Veera Sundaram Sankaran <veeras@xxxxxxxxxxxxxx>

Looks good. I appreciate you addressing my earlier comments and
sending this out again!

Reviewed-by: John Stultz <john.stultz@xxxxxxxxxx>

thanks
-john
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