Re: [PATCH] drm/vc4: Ignore alpha on primary plane

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Mar 02, 2018 at 04:39:22PM +0200, Ville Syrjälä wrote:
> On Fri, Mar 02, 2018 at 01:32:40AM +0100, Stefan Schake wrote:
> > We allow alpha formats on the primary plane but a partially transparent
> > framebuffer will cause a corrupted display. With this change black pixels
> > are output instead, in line with the behavior for other DRM drivers.
> > 
> > Signed-off-by: Stefan Schake <stschake@gmail.com>
> > ---
> > Test program is available at https://github.com/stschake/vc4-alpha-test
> > 
> >  drivers/gpu/drm/vc4/vc4_plane.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/vc4/vc4_plane.c b/drivers/gpu/drm/vc4/vc4_plane.c
> > index 61ad955..8c829fa 100644
> > --- a/drivers/gpu/drm/vc4/vc4_plane.c
> > +++ b/drivers/gpu/drm/vc4/vc4_plane.c
> > @@ -521,6 +521,7 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
> >  	u32 ctl0_offset = vc4_state->dlist_count;
> >  	const struct hvs_format *format = vc4_get_hvs_format(fb->format->format);
> >  	int num_planes = drm_format_num_planes(format->drm);
> > +	bool primary_plane = state->crtc->primary == plane;
> >  	u32 scl0, scl1, pitch0;
> >  	u32 lbm_size, tiling;
> >  	unsigned long irqflags;
> > @@ -620,8 +621,12 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
> >  
> >  	/* Position Word 2: Source Image Size, Alpha Mode */
> >  	vc4_state->pos2_offset = vc4_state->dlist_count;
> > +	/* We do not enable the HVS background color fill so the primary plane
> > +	 * must be opaque to avoid display artifacts. Achieve this by always
> > +	 * using fixed alpha (initialized to 0xff above) on the primary plane.
> > +	 */
> >  	vc4_dlist_write(vc4_state,
> > -			VC4_SET_FIELD(fb->format->has_alpha ?
> > +			VC4_SET_FIELD(fb->format->has_alpha && !primary_plane ?
> 
> If you want the plane to always be opaque you shouldn't expose any
> formats with alpha.
> 
> Also what happens if one disables the primary plane? Or does the driver
> not allow that?

Or just makes the plane not cover the entire screen?

-- 
Ville Syrjälä
Intel OTC
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