Re: [PATCH v4 1/6] drm: allow DRM_MODE_PAGE_FLIP_ASYNC for atomic commits

[Simon Ser]

On Tuesday, July 4th, 2023 at 19:06, Sebastian Wick <sebastian.wick@xxxxxxxxxx> wrote:

> > + * 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.
> > + *
> > + * Note, some hardware might need to perform one last synchronous page-flip
> > + * before being able to switch to asynchronous page-flips. As an exception,
> > + * the driver will return success even though that first page-flip is not
> > + * asynchronous.
> 
> What would happen if one commits another async KMS update before the
> first page flip? Does one receive EAGAIN, does it amend the previous
> commit? What happens to the timing feedback?
> 
> This seems really risky to include tbh. I would prefer if we would not
> add such special cases for now.

This is not a new case, i915 already does this with the legacy API to
address some hw issues. Sadly I don't think we can do anything about
it.