Re: [RFC] drm: return int error code from mode_fixup

[Sam Ravnborg <sam@ravnborg.org>]

On Tue, Jul 13, 2021 at 07:44:12PM +0200, Daniel Vetter wrote:
> On Tue, Jul 13, 2021 at 7:14 PM Grace An <gracan@codeaurora.org> wrote:
> > When CONFIG_PROVE_LOCKING is defined, the kernel randomly injects
> > -EDEADLK errors for all the ww_mutex. This results in
> > drm_atomic_get_private_obj_state randomly returning -EDEADLK.
> > However, the mode_fixup functions do not propagate these error
> > codes and return false, causing the atomic commit to fail with
> > -EINVAL instead of retrying.
> >
> > Change encoder, crtc, and bridge mode_fixup functions to return
> > an int instead of a boolean to indicate success or failure. If
> > any of these functions fail, the mode_fixup function now returns
> > the provided integer error code instead of -EINVAL.
> >
> > This change needs modifications across drivers, but before submitting
> > the entire change, we want to get feedback on this RFC.
> >
> > Signed-off-by: Grace An <gracan@codeaurora.org>
> 
> Why don't you just use the various atomic_check hooks we have for
> this? There you get passed the state and everything, have a full int
> return value, and things actually work.
> 
> ->mode_fixup is for compatibility with legacy crtc modeset helpers
> from the pre-atomic times. If the kerneldoc isn't clear yet, please do
> a patch to fix that up so that @mode_fixup points at the relevant
> @atomic_check as the recommended function.
Agreed, and we need to document this better.

I have posted the following patch to make it more obvious that
mode_fixup is deprecated.
https://lore.kernel.org/dri-devel/20210713193257.958852-1-sam@ravnborg.org/T/#u

	Sam