[PATCH 1/3] RFC: drm: Restrict vblank ioctl to master

[Mario Kleiner]

On 05/05/2017 09:35 PM, Daniel Vetter wrote:
> On Mon, Jul 25, 2016 at 1:15 PM, Rainer Hochecker <fernetmenta at kodi.tv> wrote:
>> Am 25.07.2016 08:38 schrieb "Michel Dänzer" <michel at daenzer.net>:
>>>
>>> On 13.07.2016 18:49, Rainer Hochecker wrote:
>>>> We have been using this for years now and did not observe issues you
>>>> mentioned. I would be surprised if a child window refreshes in a
>>>> different rate than the main window
>>>
>>> The Xorg driver decides which CRTC to synchronize with based on the
>>> window geometry. For a window with no visible geometry, it may choose a
>>> different CRTC than for the visible output window. In the case of DRI3,
>>> the Xorg Present extension code may even fall back to the fake CRTC in
>>> that case, which only generates a fake vblank event once every second.
>>>
>>>
>>> --
>>> Earthling Michel Dänzer               |               http://www.amd.com
>>> Libre software enthusiast             |             Mesa and X developer
>>>
>>
>> That means that we won't have a solution for X11 with EGL for Intel systems
>> anymore.
>
> I didn't know about this, but a proper EGL extension, implemented on
> X11 exists already:
>
> https://codereview.chromium.org/2867513002/
>
> It's not in the khronos registry, but mesa implements it, and
> semantics match oml_sync (and wayland present), so we already have the
> proper extension to implement this without digging around in device
> files and making a guess about which pipe you might be running on.
>
> Cheers, Daniel
>

Yep. The weird thing about that extension is that it only implements the 
query vblank count/timestamp part of GLX_OML_sync_control. Sounds like 
the least useful bit of all in isolation, although the extension as a 
whole could be useful, just as on GLX. Also note this comment on that 
commit referenced by Daniel from just 2 hours ago:

"marcheu 2 hours, 35 minutes ago (2017-05-05 18:52:45 UTC) #10
lgtm

By the way, there is discussion on dropping this extension from mesa. 
You should let Chad know if you need it in the long run. Chrome OS 
stopped requiring it when we switched to freon."

Cc'ing Chad Versace on the off-chance he is the mentioned Chad.

Also, the VDPAU api for video playback implements functions for precise 
timing of video frame presentation. I don't have any practical 
experience with them, but iirc Mesa's VDPAU video presentation api 
implements those via DRI3/Present extension, so hooks into drmWaitVblank 
et al. If Kodi uses VDPAU for playback, it could use those conveniently 
for timing.

-mario