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

[Jesse Barnes]

On 10/13/2015 02:24 PM, 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);
>  		I915_WRITE(DSPSURF(plane), 0);
>  		POSTING_READ(reg);
>  		return;

For some reason this rings a bell.  Paulo did you work on something
similar awhile back?

Anyway, hooray for fixing bugs!

Reviewed-by: Jesse Barnes <jbarnes at virtuousgeek.org>

Thanks,
Jesse