[PATCH] drm: rcar-du: Revert "drm: rcar-du: Use __drm_atomic_helper_plane_reset instead of copying the logic"

[Alexandru-Cosmin Gheorghe]

Hi Kieran,

Sorry for that and thanks for getting to the bottom of it.


On Fri, Sep 14, 2018 at 11:28:05PM +0100, Kieran Bingham wrote:
> Hi Laurent,
> 
> I've looked through a bit further to try to understand this issue and I
> think I have identified a possible/probable cause.
> 
> Before commit 161ad653d6c9, we *always* set the plane->state->alpha as
> DRM_BLEND_ALPHA_OPAQUE. (0xffff)
> 
> After this commit, the __drm_atomic_helper_plane_reset() call will only
> set state->alpha to 0xffff if the alpha_property is set:
> 
>         if (plane->alpha_property)
>                 state->alpha = plane->alpha_property->values[1];
> 
> Then the state->alpha value is always referenced in
> rcar_du_vsp_plane_setup() and passed to the VSP for that layer.
> 
> 
> We can see in rcar_du_planes_init(), that all OVERLAY planes are
> configured to have this propery with a call to
> drm_plane_create_alpha_property(&plane->plane); however - the PRIMARY
> plane is skipped over before setting this.
> 
> 
> I believe I recall seeing that the kms-test-planeposition.py
> successfully showed other planes which were not the back one (I'm now
> going from hazy memory of this afternoon - but I am fairly sure I saw this)
> 
> 
> This implies that the primary planes are being incorrectly configured -
> but the overlay planes are still functioning as expected.
> 
> So I believe we could move the call to create the alpha property:
> 	drm_plane_create_alpha_property(&plane->plane);
> 
> to occur before the if (type == DRM_PLANE_TYPE_PRIMARY) continue; statement.
> 

I don't see any reson why the primary plane shouldn't advertise an
alpha as well.

> It may or may not make sense to have alpha blending support on the
> PRIMARY plane. At the risk of sounding silly - can we have anything else
> behind the PRIMARY plane ? (I doubt this, I don't think we have any
> extra layers hiding anywhere)

I think the same question could apply to situations where PRIMARY is
disabled and you have just one OVERLAY plane enabled.

> 
> Otherwise, I think we would need to intercept the configuration of the
> alpha blending and make sure that all PRIMARY planes are configured to
> be fully opaque in our layers. I think this is happening in
> rcar_du_vsp_plane_setup().
> 
> But rather than put in a conditional in there, I think I'd rather just
> initialise the plane->state->alpha = DRM_BLEND_ALPHA_OPAQUE in our
> rcar_du_vsp_plane_reset() call and be done with it.

I think you could do more and just go in
__drm_atomic_helper_plane_reset and always initializes plane->alpha
with DRM_BLEND_ALPHA_OPAQUE, this way nobody else hits this problem.

> 
> Anyway - just some musings and thoughts at this stage, we can
> investigate in more detail next week.
> 
> --
> Regards
> 
> Kieran
> 
> 
> On 14/09/18 21:09, Kieran Bingham wrote:
> > Commit: 161ad653d6c9 ("drm: rcar-du: Use __drm_atomic_helper_plane_reset
> > instead of copying the logic") causes a regression in the R-Car DU
> > display driver, and prevents any output from being displayed.
> > 
> > The display appears to function correctly but only a black screen is
> > ever visible.
> > 
> > Revert the commit.
> > 
> > Signed-off-by: Kieran Bingham <kieran.bingham+renesas at ideasonboard.com>
> > 
> > ---
> > 
> > Looking through the code, the reason for this issue isn't particularly
> > obvious - and will need some further exploration, which I can't look at
> > until Tuesday. So I'm posting this revert patch to
> > 
> >  A) Report the issue
> >  B) Provide a temporary fix
> > 
> > I suspect either the initial alpha value is not set correctly or setting
> > 
> >          state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
> > 
> > causes some side effect perhaps. There's not much else that could be
> > different between the helper, and the original code.
> > 
> >  drivers/gpu/drm/rcar-du/rcar_du_plane.c | 6 ++++--
> >  drivers/gpu/drm/rcar-du/rcar_du_vsp.c   | 5 ++++-
> >  2 files changed, 8 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> > index 9e07758a755c..5c2462afe408 100644
> > --- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> > +++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> > @@ -686,12 +686,14 @@ static void rcar_du_plane_reset(struct drm_plane *plane)
> >  	if (state == NULL)
> >  		return;
> >  
> > -	__drm_atomic_helper_plane_reset(plane, &state->state);
> > -
> >  	state->hwindex = -1;
> >  	state->source = RCAR_DU_PLANE_MEMORY;
> >  	state->colorkey = RCAR_DU_COLORKEY_NONE;
> >  	state->state.zpos = plane->type == DRM_PLANE_TYPE_PRIMARY ? 0 : 1;
> > +
> > +	plane->state = &state->state;
> > +	plane->state->alpha = DRM_BLEND_ALPHA_OPAQUE;
> > +	plane->state->plane = plane;
> >  }
> >  
> >  static int rcar_du_plane_atomic_set_property(struct drm_plane *plane,
> > diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> > index 4576119e7777..3170b126cfba 100644
> > --- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> > +++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> > @@ -341,8 +341,11 @@ static void rcar_du_vsp_plane_reset(struct drm_plane *plane)
> >  	if (state == NULL)
> >  		return;
> >  
> > -	__drm_atomic_helper_plane_reset(plane, &state->state);
> > +	state->state.alpha = DRM_BLEND_ALPHA_OPAQUE;
> >  	state->state.zpos = plane->type == DRM_PLANE_TYPE_PRIMARY ? 0 : 1;
> > +
> > +	plane->state = &state->state;
> > +	plane->state->plane = plane;
> >  }
> >  
> >  static const struct drm_plane_funcs rcar_du_vsp_plane_funcs = {
> > 

-- 
Cheers,
Alex G