Re: [PATCH v7 2/9] drm: Support per-plane async flip configuration

[André Almeida]

Em 18/06/2024 07:07, Dmitry Baryshkov escreveu:
> On Tue, 18 Jun 2024 at 12:38, Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx> wrote:
> > On Tue, 18 Jun 2024, André Almeida <andrealmeid@xxxxxxxxxx> wrote:
> > > Drivers have different capabilities on what plane types they can or
> > > cannot perform async flips. Create a plane::async_flip field so each
> > > driver can choose which planes they allow doing async flips.
> > >
> > > Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
> > > ---
> > >   include/drm/drm_plane.h | 5 +++++
> > >   1 file changed, 5 insertions(+)
> > >
> > > diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> > > index 9507542121fa..0bebc72af5c3 100644
> > > --- a/include/drm/drm_plane.h
> > > +++ b/include/drm/drm_plane.h
> > > @@ -786,6 +786,11 @@ struct drm_plane {
> > >         * @kmsg_panic: Used to register a panic notifier for this plane
> > >         */
> > >        struct kmsg_dumper kmsg_panic;
> > > +
> > > +     /**
> > > +      * @async_flip: indicates if a plane can do async flips
> > > +      */
> >
> > When is it okay to set or change the value of this member?
> >
> > If you don't document it, people will find creative uses for this.
>
> Maybe it's better to have a callback instead of a static field? This
> way it becomes clear that it's only relevant at the time of the
> atomic_check().

So we would have something like bool (*async_flip) for struct 
drm_plane_funcs I suppose. Then each driver will implement this function 
and check on runtime if it should flip or not, right?

I agree that it makes more clear, but as far as I can see this is not 
something that is subject to being changed at runtime at all, so it 
seems a bit overkill to me to encapsulate a static information like 
that. I prefer to improve the documentation on the struct member to see 
if this solves the problem. What do you think of the following comment:

/**
 * @async_flip: indicates if a plane can perform async flips. The
 * driver should set this true only for planes that the hardware
 * supports flipping asynchronously. It may not be changed during
 * runtime. This field is checked inside drm_mode_atomic_ioctl() to
 * allow only the correct planes to go with DRM_MODE_PAGE_FLIP_ASYNC.
 */