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@xxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Testcase: igt/kms_plane/plane-clipping-pipe-A-planes
> Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxxxx>
> + (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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