[PATCH 0/6] drm: Explicit target vblank seqno for page flips

[Ville Syrjälä]

On Thu, Aug 04, 2016 at 11:12:27AM +0100, Daniel Stone wrote:
> On 4 August 2016 at 11:01, Michel Dänzer <michel at daenzer.net> wrote:
> > On 04.08.2016 18:51, Daniel Stone wrote:
> >> On 4 August 2016 at 04:39, Michel Dänzer <michel at daenzer.net> wrote:
> >>> Patch 6 extends the ioctl with new flags, which allow userspace to
> >>> explicitly specify the target vblank seqno. This can also avoid delaying
> >>> flips in some cases where we are already in the target vertical blank
> >>> period when the ioctl is called.
> >>
> >> Is there open userspace for this?
> >
> > Sure, referenced in patch 6:
> >
> > https://cgit.freedesktop.org/~daenzer/xf86-video-ati/commit/?id=fc884a8af25345c32bd4104c864ecfeb9bb3db9b
> >
> > https://cgit.freedesktop.org/~daenzer/xf86-video-amdgpu/commit/?id=b8631a9ba49c0d0ebe5dcd1dbfb68fcfe907296f
> >
> >
> >> What's the behaviour vs. modeset: does the modeset request block until
> >> the last-requested flip is complete? If so, is there some kind of upper
> >> bound on the number of blank periods to wait for?
> >
> > Did you read the patch? :)
> 
> Nope, for some reason my mailer decided it didn't like it, but I did
> find it in the archives.
> 
> > The only change compared to the existing ioctl is that userspace can ask
> > for a flip to take effect in the current vblank seqno. The code added by
> > the patch checks for target vblank seqno > current vblank seqno + 1 and
> > returns -EINVAL in that case. This is also documented in drm_mode.h.
> 
> Is there any particular benefit to having split absolute/relative
> modes in this case? Personally I'm struggling to see the use of
> relative.

Last time I read the egl spec it specified swap interval as
RELATIVE=<interval>, whereas GLX_whatever specified the more sensible
ABSOLUTE=<last+interval> behaviour.

I suppose that means Mesa is technically not egl compliant with DRI2/3.

> 
> >> Is all this tested somewhere?
> >
> > Yes, I've been using it for a while on all my machines.
> 
> I mean in a test suite. :)
> 
> Cheers,
> Daniel
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-- 
Ville Syrjälä
Intel OTC