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

[Daniel Vetter]

On Thu, Aug 04, 2016 at 09:31:20AM +0300, Jani Nikula wrote:
> On Wed, 03 Aug 2016, Chris Wilson <chris at chris-wilson.co.uk> 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>
> 
> Cc: stable at vger.kernel.org

fbc isn't enabled by default, so imo no.
-Daniel

> 
> ?
> 
> > ---
> >  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)
> > +{
> > +#ifdef CONFIG_INTEL_IOMMU
> > +	/* WaFbcTurnOffFbcWhenHyperVisorIsUsed:skl */
> > +	if (intel_iommu_gfx_mapped && IS_SKYLAKE(dev_priv)) {
> > +		DRM_INFO("Disabling framebuffer compression (FBC) to prevent screen flicker with VT-d enabled\n");
> > +		return true;
> > +	}
> > +#endif
> > +
> > +	return false;
> > +}
> > +
> >  /**
> >   * intel_fbc_init - Initialize FBC
> >   * @dev_priv: the i915 device
> > @@ -1252,6 +1268,9 @@ void intel_fbc_init(struct drm_i915_private *dev_priv)
> >  	fbc->active = false;
> >  	fbc->work.scheduled = false;
> >  
> > +	if (need_fbc_wa(dev_priv))
> > +		mkwrite_device_info(dev_priv)->has_fbc = false;
> > +
> >  	i915.enable_fbc = intel_sanitize_fbc_option(dev_priv);
> >  	DRM_DEBUG_KMS("Sanitized enable_fbc value: %d\n", i915.enable_fbc);
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center
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> Intel-gfx at lists.freedesktop.org
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch