[PATCH] drm/atomic: Add sanity checks to drm_atomic_helper_async_commit()

[Eric Anholt]

Boris Brezillon <boris.brezillon at bootlin.com> writes:

> ->atomic_async_update() requires that drivers update the plane->state
> object before returning. Make sure at least common properties have been
> updated.
>
> Cc: Gustavo Padovan <gustavo at padovan.org>
> Signed-off-by: Boris Brezillon <boris.brezillon at bootlin.com>
> ---
> Hello,
>
> This is a problem I had when debugging the VC4 ->atomic_async_update()
> implementation. The function was not updating plane->fb as it's
> supposed thus leaving plane->state->fb in an inconsistent state after
> each async update.
>
> Not sure if such WARN_ON_ONCE() are accepted in the core though, so
> I'll maintainers decide whether this is relevant or not and whether
> they prefer to have WARN_ON() or DRM_ERROR() messages.

I'm a huge fan of this kind of safety check.  FWIW,

Acked-by: Eric Anholt <eric at anholt.net>
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