[Intel-gfx] [PATCH] Revert "drm/atomic: document and enforce rules around "spurious" EBUSY"

[Simon Ser]

On Wednesday, February 10th, 2021 at 2:16 PM, Daniel Vetter <daniel at ffwll.ch> wrote:

> On Tue, Feb 09, 2021 at 04:14:01PM -0800, Manasi Navare wrote:
>
> > These additional checks added to avoid EBUSY give unnecessary WARN_ON
> > in case of big joiner used in i915 in which case even if the modeset
> > is requested on a single pipe, internally another consecutive
> > pipe is stolen and used to drive half of the transcoder timings.
> > So in this case it is expected that requested crtc and affected crtcs
> > do not match. Hence the added WARN ON becomes irrelevant.

The WARN_ON only happens if allow_modeset == false. If allow_modeset == true,
then the driver is allowed to steal an unrelated pipe.

Maybe i915 is stealing a pipe without allow_modeset?

> Nope. We can maybe rework this so that i915 can do stuff under the hood,
> but wrt uapi this was the thing we discussed with compositors. Without
> such a guarantee atomic is defacto broken from a compositor pov.

Agreed.