[Intel-gfx] [PATCH v2] drm/i915/fbc: FBC causes display flicker when VT-d is enabled on Skylake

[Chris Wilson]

On Thu, Aug 04, 2016 at 09:57:11AM +0300, Ville Syrjälä wrote:
> On Wed, Aug 03, 2016 at 05:16:42PM +0100, Chris Wilson wrote:
> > Erratum SKL075: Display Flicker May Occur When Both VT-d And FBC Are Enabled
> > 
> > "Display flickering may occur when both FBC (Frame Buffer Compression)
> > and VT - d (Intel® Virtualization Technology for Directed I/O) are enabled
> > and in use by the display controller."
> > 
> > Ville found the w/a name in the database:
> > WaFbcTurnOffFbcWhenHyperVisorIsUsed:skl
> > 
> > v2: Log when the quirk is applied.
> > v3: Ensure i915.enable_fbc is false when !HAS_FBC()
> > v4: Fix function name after rebase
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_fbc.c | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
> > index 8147eb9e8475..b673c7c54a46 100644
> > --- a/drivers/gpu/drm/i915/intel_fbc.c
> > +++ b/drivers/gpu/drm/i915/intel_fbc.c
> > @@ -1229,12 +1229,28 @@ static int intel_sanitize_fbc_option(struct drm_i915_private *dev_priv)
> >  	if (i915.enable_fbc >= 0)
> >  		return !!i915.enable_fbc;
> >  
> > +	if (!HAS_FBC(dev_priv))
> > +		return 0;
> > +
> >  	if (IS_BROADWELL(dev_priv))
> >  		return 1;
> >  
> >  	return 0;
> >  }
> >  
> > +static bool need_fbc_wa(struct drm_i915_private *dev_priv)
> 
> need_fbc_vtd_wa() perhaps?

Right now, yes. I left it open just in case - but that's most likely a
false hope.

> > +{
> > +#ifdef CONFIG_INTEL_IOMMU
> > +	/* WaFbcTurnOffFbcWhenHyperVisorIsUsed:skl */
> > +	if (intel_iommu_gfx_mapped && IS_SKYLAKE(dev_priv)) {
> 
> BXT needs this as well AFAICS.

Will IS_GEN9() suit? +skl,bxt in the description.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre