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

[Alexandru-Cosmin Gheorghe <Alexandru-Cosmin.Gheorghe@arm.com>]

Hi Kieran,

On Mon, Sep 17, 2018 at 11:56:23AM +0100, Kieran Bingham wrote:
> Hi Alexandru,
> 
> On 17/09/18 10:10, Alexandru-Cosmin Gheorghe wrote:
> > Hi Kieran,
> > 
> > Sorry for that and thanks for getting to the bottom of it.
> 
> No worries,
> 
> 
> > 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.
> 
> 
> OK - so I think we perhaps should make sure that we enable alpha for our
> primary plane in rcar-du.
> 
> 
> >> 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.
> 
> I think this sounds like a good thing too.
> 
> Is DRM_BLEND_ALPHA_OPAQUE a suitable initial value for all of the other
> users of the helper ?
> 
> I suspect the answer is yes, but I'll try to do a bit of digging through
> the other drivers tomorrow.
>

Yes, but it doesn't hurt for another pair of eyes to have a look.
 
> I presume we could then just remove the conditional check and always
> initialise to OPAQUE ...
> 
> Or otherwise perhaps maybe initialising as an 'else' if no alpha
> property is provided.
> 
> --
> Regards
> 
> Kieran
> 
> 
> 
> 
> 
> 
> >>
> >> 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@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
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