[PATCH v5 00/13] PRIME Synchronization

Dave Airlie airlied at gmail.com
Tue May 3 06:33:52 UTC 2016

On 3 May 2016 at 12:19, Alex Goins <agoins at nvidia.com> wrote:
> Sorry for all of the self-replies.
> I spent more time looking into what might be causing this (despite not being
> able to reproduce it), and found that in the Present extension's
> present_check_flip(), it doesn't use flipping if there are slave outputs. So,
> that's why it's not allowing page flipping, but that isn't due to these patches.
> Since it can't flip, it falls back to just waiting for vblank and you can get
> some ugly tearing on the native display. I still can't reproduce the choppy
> rendering, but if there is a problem it's likely something to do with
> drmWaitVBlank().
> Have you tried to see if it fails like that even without my patches? If the
> problem is with drmWaitVBlank(), it might just be that something is going wrong
> there, and adding output slaves just exposes the issue.
> It looks like since drmWaitVBlank() doesn't take in the crtc_id directly like
> drmModePageFlip(), and since there is no standard interface to do something like
> drm_intel_get_pipe_from_crtc_id(), we just make a best guess in
> drmmode_crtc_vblank_pipe(). Could be error-prone.

Okay thanks for looking into it. Yes the present behaviour is known as
we can't flip
on multiple crtcs with the current present driver API, I should post
patches to at
least clean that up.

Otherwise you are probably right wrt what is causing the choppiness, I'll try
and get some times (it might be next week) to track it down, but I don't think
it should block these patches at this point.

I'll try and finish review by the end of the week,


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