[PATCH] drm: renesas: shmobile: Add drm_panic support

[Laurent Pinchart]

Hi Dmitry,

On Wed, May 29, 2024 at 11:27:02AM +0300, Dmitry Baryshkov wrote:
> On Wed, May 29, 2024 at 04:03:20AM +0300, Laurent Pinchart wrote:
> > On Mon, May 27, 2024 at 03:34:48PM +0200, Geert Uytterhoeven wrote:
> > > Add support for the drm_panic module, which displays a message on
> > > the screen when a kernel panic occurs.
> > > 
> > > Signed-off-by: Geert Uytterhoeven <geert+renesas at glider.be>
> > > ---
> > > Tested on Armadillo-800-EVA.
> > > ---
> > >  drivers/gpu/drm/renesas/shmobile/shmob_drm_plane.c | 14 +++++++++++++-
> > >  1 file changed, 13 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/renesas/shmobile/shmob_drm_plane.c b/drivers/gpu/drm/renesas/shmobile/shmob_drm_plane.c
> > > index 07ad17d24294d5e6..9d166ab2af8bd231 100644
> > > --- a/drivers/gpu/drm/renesas/shmobile/shmob_drm_plane.c
> > > +++ b/drivers/gpu/drm/renesas/shmobile/shmob_drm_plane.c
> > > @@ -273,6 +273,13 @@ static const struct drm_plane_helper_funcs shmob_drm_plane_helper_funcs = {
> > >  	.atomic_disable = shmob_drm_plane_atomic_disable,
> > >  };
> > >  
> > > +static const struct drm_plane_helper_funcs shmob_drm_primary_plane_helper_funcs = {
> > > +	.atomic_check = shmob_drm_plane_atomic_check,
> > > +	.atomic_update = shmob_drm_plane_atomic_update,
> > > +	.atomic_disable = shmob_drm_plane_atomic_disable,
> > > +	.get_scanout_buffer = drm_fb_dma_get_scanout_buffer,
> > > +};
> > > +
> > >  static const struct drm_plane_funcs shmob_drm_plane_funcs = {
> > >  	.update_plane = drm_atomic_helper_update_plane,
> > >  	.disable_plane = drm_atomic_helper_disable_plane,
> > > @@ -310,7 +317,12 @@ struct drm_plane *shmob_drm_plane_create(struct shmob_drm_device *sdev,
> > >  
> > >  	splane->index = index;
> > >  
> > > -	drm_plane_helper_add(&splane->base, &shmob_drm_plane_helper_funcs);
> > > +	if (type == DRM_PLANE_TYPE_PRIMARY)
> > > +		drm_plane_helper_add(&splane->base,
> > > +				     &shmob_drm_primary_plane_helper_funcs);
> > > +	else
> > > +		drm_plane_helper_add(&splane->base,
> > > +				     &shmob_drm_plane_helper_funcs);
> > 
> > It's not very nice to have to provide different operations for the
> > primary and overlay planes. The documentation of
> > drm_fb_dma_get_scanout_buffer() states
> > 
> >  * @plane: DRM primary plane
> > 
> > If the intent is that only primary planes will be used to display the
> > panic message, shouldn't drm_panic_register() skip overlay planes ? It
> > would simplify drivers.
> 
> What about the drivers where all the planes are actually universal?
> In such a case the planes registered as primary can easily get replaced
> by 'overlay' planes.

Good point.

Another option, if we wanted to avoid duplicating the drm_plane_funcs,
would be to add a field to drm_plane to indicate whether the plane is
suitable for drm_panic.

I don't think this patch should be blocked just for this reason, but I'm
a bit bothered by duplicating the ops structure to indicate drm_panic
support.

> > >  
> > >  	return &splane->base;
> > >  }

-- 
Regards,

Laurent Pinchart