drm/i915/fbc: FBC causes display flicker when VT-d is enabled on Skylake

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,bxt and also dug out that it
affects Broxton.

v2: Log when the quirk is applied.
v3: Ensure i915.enable_fbc is false when !HAS_FBC()
v4: Fix function name after rebase
v5: Add Broxton to the workaround

Note for backporting to stable, we need to add
  #define mkwrite_device_info(ptr) \
	((struct intel_device_info *)INTEL_INFO(ptr))

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>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: stable@vger.kernel.org
Link: http://patchwork.freedesktop.org/patch/msgid/1470296633-20388-1-git-send-email-chris@chris-wilson.co.uk
(cherry picked from commit 36dbc4d76918d7557b686f807106dcc799174b12)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
index 6a7ad3e..3836a1c 100644 (file)
--- a/drivers/gpu/drm/i915/intel_fbc.c
+++ b/drivers/gpu/drm/i915/intel_fbc.c
@@ -1230,12 +1230,29 @@ 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_vtd_wa(struct drm_i915_private *dev_priv)
+{
+#ifdef CONFIG_INTEL_IOMMU
+       /* WaFbcTurnOffFbcWhenHyperVisorIsUsed:skl,bxt */
+       if (intel_iommu_gfx_mapped &&
+           (IS_SKYLAKE(dev_priv) || IS_BROXTON(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
@@ -1253,6 +1270,9 @@ void intel_fbc_init(struct drm_i915_private *dev_priv)
        fbc->active = false;
        fbc->work.scheduled = false;
 
+       if (need_fbc_vtd_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);