On Tue, Jun 21, 2016 at 08:25:27AM +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()
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Do we know whether this helps on other machines too? I can imagine that
the additional lookup latency just plain wreaks havoc everywhere ...
-Daniel
> ---
> 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))
> +
> #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 && 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
> @@ -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);
>
> --
> 2.8.1
>
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> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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