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

[Chris Wilson]

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 at chris-wilson.co.uk>
Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
Cc: Ville Syrjälä <ville.syrjala at 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))
+
 #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