[Intel-gfx] [PATCH] drm/i915: Disable caches for Global GTT.

[Rodrigo Vivi]

Global GTT doesn't have pat_sel[2:0] so it always point to pat_sel = 000;
So the only way to avoid screen corruptions is setting PAT 0 to Uncached.

MOCS can still be used though. But if userspace is trusting PTE for
cache selection the safest thing to do is to let caches disabled.

BSpec: "For GGTT, there is NO pat_sel[2:0] from the entry,
so RTL will always use the value corresponding to pat_sel = 000"

Reference: https://bugs.freedesktop.org/show_bug.cgi?id=85576
Cc: James Ausmus <james.ausmus at intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
---
 drivers/gpu/drm/i915/i915_gem_gtt.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index cb7adab..24b4f27 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -1911,14 +1911,27 @@ static void bdw_setup_private_ppat(struct drm_i915_private *dev_priv)
 {
 	uint64_t pat;
 
-	pat = GEN8_PPAT(0, GEN8_PPAT_WB | GEN8_PPAT_LLC)     | /* for normal objects, no eLLC */
-	      GEN8_PPAT(1, GEN8_PPAT_WC | GEN8_PPAT_LLCELLC) | /* for something pointing to ptes? */
-	      GEN8_PPAT(2, GEN8_PPAT_WT | GEN8_PPAT_LLCELLC) | /* for scanout with eLLC */
-	      GEN8_PPAT(3, GEN8_PPAT_UC)                     | /* Uncached objects, mostly for scanout */
-	      GEN8_PPAT(4, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(0)) |
-	      GEN8_PPAT(5, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(1)) |
-	      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.
+		 */
+		pat = GEN8_PPAT(0, GEN8_PPAT_UC);
+	else
+		pat = GEN8_PPAT(0, GEN8_PPAT_WB | GEN8_PPAT_LLC)     | /* for normal objects, no eLLC */
+		      GEN8_PPAT(1, GEN8_PPAT_WC | GEN8_PPAT_LLCELLC) | /* for something pointing to ptes? */
+		      GEN8_PPAT(2, GEN8_PPAT_WT | GEN8_PPAT_LLCELLC) | /* for scanout with eLLC */
+		      GEN8_PPAT(3, GEN8_PPAT_UC) | /* Uncached objects, mostly for scanout */
+		      GEN8_PPAT(4, GEN8_PPAT_WB |
+				GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(0)) |
+		      GEN8_PPAT(5, GEN8_PPAT_WB |
+				GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(1)) |
+		      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));
 
 	/* XXX: spec defines this as 2 distinct registers. It's unclear if a 64b
 	 * write would work. */
-- 
1.9.3