Re: [PATCH] drm/i915/gen9: Disable FBC on planes with a misaligned Y-offset

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

On Wed, Feb 28, 2018 at 05:36:56PM +0200, Imre Deak wrote:
> Enabling FBC on a plane having a Y-offset that isn't dividable by 4 may
> cause pipe FIFO underruns and flickers, so disable FBC on such a config.
> 
> I tried to the followings to work around the issue:
> - enable each HW work around in ILK_DPFC_CHICKEN
> - disable each compression algorithm in ILK_DPFC_CONTROL
> - disable low-power watermarks
> None of the above got rid of the problem. I haven't found this issue in
> the Bspec/WA database either.
> 
> Besides the igt testcase below (yet to be merged) an easy way to
> reproduce the issue is to enable a plane with FBC and a plane Y-offset
> not aligned to 4 and then just enable/disable FBC in a loop, keeping the
> plane enabled.
> 
> I could trigger the problem on BXT/GLK/SKL, so assume for now that it's
> only present on GEN9.
> 
> Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Testcase: igt/kms_plane/plane-clipping-pipe-A-planes
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_fbc.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
> index 38b036c499d9..224c6a795f70 100644
> --- a/drivers/gpu/drm/i915/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/intel_fbc.c
> @@ -859,6 +859,17 @@ static bool intel_fbc_can_activate(struct intel_crtc *crtc)
>  		return false;
>  	}
>  
> +	/*
> +	 * Work around a problem on GEN9 HW, where enabling FBC on a plane
> +	 * having a Y offset that isn't dividable by 4 causes FIFO underrun
> +	 * and screen ficker.

"divisible", "flicker"

> +	 */
> +	if (INTEL_GEN(dev_priv) == 9 &&

IS_GEN9()?

I do wonder about gen10+ however. GLK display pipes/planes did come
from CNL after all so it seems at least possible tht CNL suffers from
the same issue.

The patch seems sensible either way so
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> +	    (fbc->state_cache.plane.adjusted_y & 3)) {
> +		fbc->no_fbc_reason = "plane Y offset is misaligned";
> +		return false;
> +	}
> +
>  	return true;
>  }
>  
> -- 
> 2.13.2

-- 
Ville Syrjälä
Intel OTC
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