[Intel-gfx] [PATCH] 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."

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
---
 drivers/gpu/drm/i915/intel_fbc.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
index fddba1eed5ad..e47785467220 100644
--- a/drivers/gpu/drm/i915/intel_fbc.c
+++ b/drivers/gpu/drm/i915/intel_fbc.c
@@ -1230,6 +1230,18 @@ void intel_fbc_init_pipe_state(struct drm_i915_private *dev_priv)
 			dev_priv->fbc.visible_pipes_mask |= (1 << crtc->pipe);
 }
 
+static bool need_vtd_wa(struct drm_i915_private *dev_priv)
+{
+#ifdef CONFIG_INTEL_IOMMU
+	if (!intel_iommu_gfx_mapped)
+		return false;
+
+	if (INTEL_GEN(dev_priv) == 9)
+		return true;
+#endif
+	return false;
+}
+
 /**
  * intel_fbc_init - Initialize FBC
  * @dev_priv: the i915 device
@@ -1247,6 +1259,12 @@ void intel_fbc_init(struct drm_i915_private *dev_priv)
 	fbc->active = false;
 	fbc->work.scheduled = false;
 
+	if (need_vtd_wa(dev_priv)) {
+		struct intel_device_info *info =
+			(struct intel_device_info *)&dev_priv->info;
+		info->has_fbc = false;
+	}
+
 	if (!HAS_FBC(dev_priv)) {
 		fbc->no_fbc_reason = "unsupported by this chipset";
 		return;
-- 
2.8.1