drm/i915: Set up an MTRR covering the GTT at driver load.

We'd love to just be using PAT, but even on chips with PAT it gets disabled
sometimes due to an errata.  It would probably be better to have pat_enabled
exported and only bother with this when !pat_enabled.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@linux.ie>

1 files changed, 24 insertions, 5 deletions

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index ee64b7301f67..1e01e7847155 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -966,10 +966,6 @@ static int i915_load_modeset_init(struct drm_device *dev)
 	if (ret)
 		goto kfree_devname;
 
-        dev_priv->mm.gtt_mapping =
-		io_mapping_create_wc(dev->agp->base,
-				     dev->agp->agp_info.aper_size * 1024*1024);
-
 	/* Allow hardware batchbuffers unless told otherwise.
 	 */
 	dev_priv->allow_batchbuffer = 1;
@@ -1081,6 +1077,23 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 		goto free_priv;
 	}
 
+        dev_priv->mm.gtt_mapping =
+		io_mapping_create_wc(dev->agp->base,
+				     dev->agp->agp_info.aper_size * 1024*1024);
+	/* 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
+	 * MTRR if present.  Even if a UC MTRR isn't present.
+	 */
+	dev_priv->mm.gtt_mtrr = mtrr_add(dev->agp->base,
+					 dev->agp->agp_info.aper_size *
+					 1024 * 1024,
+					 MTRR_TYPE_WRCOMB, 1);
+	if (dev_priv->mm.gtt_mtrr < 0) {
+		DRM_INFO("MTRR allocation failed\n.  Graphics "
+			 "performance may suffer.\n");
+	}
+
 #ifdef CONFIG_HIGHMEM64G
 	/* don't enable GEM on PAE - needs agp + set_memory_* interface fixes */
 	dev_priv->has_gem = 0;
@@ -1145,8 +1158,14 @@ int i915_driver_unload(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
+	io_mapping_free(dev_priv->mm.gtt_mapping);
+	if (dev_priv->mm.gtt_mtrr >= 0) {
+		mtrr_del(dev_priv->mm.gtt_mtrr, dev->agp->base,
+			 dev->agp->agp_info.aper_size * 1024 * 1024);
+		dev_priv->mm.gtt_mtrr = -1;
+	}
+
 	if (drm_core_check_feature(dev, DRIVER_MODESET)) {
-		io_mapping_free(dev_priv->mm.gtt_mapping);
 		drm_irq_uninstall(dev);
 	}