1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index b672b843fd5e..728938f02341 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -1902,6 +1902,22 @@ static void bdw_setup_private_ppat(struct drm_i915_private *dev_priv)
               GEN8_PPAT(6, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(2)) |
               GEN8_PPAT(7, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(3));
 
+        if (!USES_PPGTT(dev_priv->dev))
+                /* Spec: "For GGTT, there is NO pat_sel[2:0] from the entry,
+                 * so RTL will always use the value corresponding to
+                 * pat_sel = 000".
+                 * So let's disable cache for GGTT to avoid screen corruptions.
+                 * MOCS still can be used though.
+                 * - System agent ggtt writes (i.e. cpu gtt mmaps) already work
+                 * before this patch, i.e. the same uncached + snooping access
+                 * like on gen6/7 seems to be in effect.
+                 * - So this just fixes blitter/render access. Again it looks
+                 * like it's not just uncached access, but uncached + snooping.
+                 * So we can still hold onto all our assumptions wrt cpu
+                 * clflushing on LLC machines.
+                 */
+                pat = GEN8_PPAT(0, GEN8_PPAT_UC);
+
         /* XXX: spec defines this as 2 distinct registers. It's unclear if a 64b
          * write would work. */
         I915_WRITE(GEN8_PRIVATE_PAT, pat);