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

[Daniel Stone]

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.

>> 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