[Intel-gfx] [PATCH] drm/i915: respect previous reg values on primary plane disable

[Chris Wilson]

On Wed, Oct 14, 2015 at 03:07:41PM +0300, Ville Syrjälä wrote:
> On Tue, Oct 13, 2015 at 02:24:41PM -0700, Kevin Strasser wrote:
> > On HSW the crc differs between black and disabled primary planes, causing an
> > assert to fail in the kms_universal_plane test. It seems that things like gamma
> > correction are causing the black primary plane case to result in a brighter
> > color than the disabled primary plane case.
> > 
> > Only toggle the enable bit instead of clearing the control register, making the
> > disable path more similar to that of the sprite plane.
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89331
> > Testcase: igt/kms_universal_plane
> > Signed-off-by: Kevin Strasser <kevin.strasser at linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_display.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index cddb0c6..b6164d8e 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -2829,7 +2829,7 @@ static void ironlake_update_primary_plane(struct drm_crtc *crtc,
> >  	int pixel_size;
> >  
> >  	if (!visible || !fb) {
> > -		I915_WRITE(reg, 0);
> > +		I915_WRITE(reg, I915_READ(reg) & ~DISPLAY_PLANE_ENABLE);
> 
> Eh, what now? We've been trying to eliminate these nasty RMWs.
> 
> Are you saying that if we disabled the plane, but leave the "pass plane
> data through gamma" it still affects the output for any pixel "covered"
> by the disabled plane?

What I thought was being said was that if a plane is set to black (but
with gamma enabled on the pipe) then a different CRC is produced
compared to when the pipe is completely disabled (no plane at all). It
sounded to me like a test case failure.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre