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

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

On Thu, Aug 04, 2016 at 08:03:09AM +0100, Chris Wilson wrote:
> 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@chris-wilson.co.uk>
> > > Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> > > Cc: Ville Syrjälä <ville.syrjala@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.

Looks like KBL doesn't need this w/a.

-- 
Ville Syrjälä
Intel OTC
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