[PATCH v2 4/6] drm: allow DRM_MODE_PAGE_FLIP_ASYNC for atomic commits

[Simon Ser]

On Wednesday, August 31st, 2022 at 09:50, Pekka Paalanen <ppaalanen at gmail.com> wrote:

> > diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> > index 86a292c3185a..cce1a1bea645 100644
> > --- a/include/uapi/drm/drm_mode.h
> > +++ b/include/uapi/drm/drm_mode.h
> > @@ -942,6 +942,10 @@ struct hdr_output_metadata {
> > * Request that the page-flip is performed as soon as possible, ie. with no
> > * delay due to waiting for vblank. This may cause tearing to be visible on
> > * the screen.
> > + *
> > + * When used with atomic uAPI, the driver will return an error if the hardware
> > + * doesn't support performing an asynchronous page-flip for this update.
> > + * User-space should handle this, e.g. by falling back to a regular page-flip.
> > */
> > #define DRM_MODE_PAGE_FLIP_ASYNC 0x02
> > #define DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE 0x4
> 
> Hi Simon,
> 
> recalling what Ville explained that enabling async flips might require
> one more sync flip first, how is that supposed to work?
> 
> A TEST_ONLY commit is not allowed to change hardware state, and a
> failing real commit is not allowed to change hardware state either
> (right?), therefore a failing async flip cannot prepare the next flip
> to be async, meaning async will never work.

I'd blame it on bad hw, and make it one special quirk in the driver,
just like it does now.

Ville, thoughts?