[Intel-gfx] [PATCH 3/3] drm/i915: Don't do MTRR setup if PAT is enabled

Adam Jackson ajax at redhat.com
Tue Mar 13 17:22:13 CET 2012

Some newer BIOSes are shipping with all MTRRs already populated.  These
BIOSes are all on machines with sufficiently new CPUs that the
referenced errata doesn't apply anyway, so just don't try to claim the

Signed-off-by: Adam Jackson <ajax at redhat.com>
 drivers/gpu/drm/i915/i915_dma.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index d52f4a5..cc0e70a 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -43,6 +43,7 @@
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <acpi/video.h>
+#include <asm/pat.h>
 static void i915_write_hws_pga(struct drm_device *dev)
@@ -1897,6 +1898,11 @@ static void
 i915_mtrr_setup(struct drm_i915_private *dev_priv, unsigned long base,
 		unsigned long size)
+#if defined(CONFIG_X86_PAT)
+	if (pat_enabled)
+		return;
 	/* Set up a WC MTRR for non-PAT systems.  This is more common than
 	 * one would think, because the kernel disables PAT on first
 	 * generation Core chips because WC PAT gets overridden by a UC

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