Re: [PATCH v3] drm/i915/fbc: FBC causes display flicker when VT-d is enabled on Skylake

["Zanoni, Paulo R" <paulo.r.zanoni@intel.com>]

Em Ter, 2016-06-21 às 08:25 +0100, Chris Wilson escreveu:
> 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()
> 
> 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/i915_drv.h  |  2 ++
>  drivers/gpu/drm/i915/intel_fbc.c | 19 +++++++++++++++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h
> b/drivers/gpu/drm/i915/i915_drv.h
> index 89298d3ad94b..f1e9fd07d441 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2586,6 +2586,8 @@ struct drm_i915_cmd_table {
>  #define INTEL_GEN(p)	(INTEL_INFO(p)->gen)
>  #define INTEL_DEVID(p)	(INTEL_INFO(p)->device_id)
>  
> +#define mkwrite_intel_info(p) ((struct intel_device_info
> *)INTEL_INFO(p))

So why don't we un-const struct intel_device_info?

> +
>  #define REVID_FOREVER		0xff
>  #define INTEL_REVID(p)	(__I915__(p)->drm.pdev->revision)
>  
> diff --git a/drivers/gpu/drm/i915/intel_fbc.c
> b/drivers/gpu/drm/i915/intel_fbc.c
> index ac26aa8be9d0..fd5865d80bec 100644
> --- a/drivers/gpu/drm/i915/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/intel_fbc.c
> @@ -1238,12 +1238,28 @@ 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 

The doc says: "Workaround: Disable FBC when VT-d superpage is used.".
My iommu-fu is not strong enough for me to be 100% sure that the
variable above corresponds to that. I'll just have to take your word
here.


> && IS_SKYLAKE(dev_priv)) {

The WA also applies to BXT, and pre-prod KBL, so I suppose at least a
check for BXT would be good.

> +		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
> @@ -1261,6 +1277,9 @@ void intel_fbc_init(struct drm_i915_private
> *dev_priv)
>  	fbc->active = false;
>  	fbc->work.scheduled = false;
>  
> +	if (need_fbc_wa(dev_priv))
> +		mkwrite_intel_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);
>  
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