[PATCH 2/3] drm/vc4: Check if plane requires background fill

[Ville Syrjälä]

On Tue, Mar 06, 2018 at 04:10:33PM -0800, Eric Anholt wrote:
> Ville Syrjälä <ville.syrjala at linux.intel.com> writes:
> 
> > On Tue, Mar 06, 2018 at 02:48:38AM +0100, Stefan Schake wrote:
> >> Considering a single plane only, we have to enable background color
> >> when the plane has an alpha format and could be blending from the
> >> background or when it doesn't cover the entire screen.
> >> 
> >> Signed-off-by: Stefan Schake <stschake at gmail.com>
> >> ---
> >>  drivers/gpu/drm/vc4/vc4_drv.h   |  6 ++++++
> >>  drivers/gpu/drm/vc4/vc4_plane.c | 15 ++++++++++++++-
> >>  2 files changed, 20 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h
> >> index fefa166..7cc6390 100644
> >> --- a/drivers/gpu/drm/vc4/vc4_drv.h
> >> +++ b/drivers/gpu/drm/vc4/vc4_drv.h
> >> @@ -302,6 +302,12 @@ struct vc4_hvs {
> >>  
> >>  struct vc4_plane {
> >>  	struct drm_plane base;
> >> +
> >> +	/* Set when the plane has per-pixel alpha content or does not cover
> >> +	 * the entire screen. This is a hint to the CRTC that it might need
> >> +	 * to enable background color fill.
> >> +	 */
> >> +	bool needs_bg_fill;
> >
> > Looks to me like that should really be a bitmask (or something similar)
> > in the crtc state.
> 
> Why?
> 
> In particular, VC4 really doesn't have a fixed number of planes, and the
> fact that we're exposing just a handful so far is probably a bug.

The problem is that this seems to clobber the device state from the
.atomic_check() hook. So if you do a CHECK_ONLY atomic ioctl (or
some later check simply fails and the operation is aborted) you've
already modified the state of the device, and some later operation
may then end up doing the wrong thing.

I guess you could track this in the plane struct like here, but as
with the actual hardware state that shouldn't get modified until
we're sure the checked state is really meant to be commited to the
hardware.

-- 
Ville Syrjälä
Intel OTC