Am 04.02.2015 um 02:19 schrieb Michel Dänzer:
From: Michel Dänzer <michel.daenzer@xxxxxxx>
Doing so can cause things to become slow.
Print a warning at compile time and an informative message at runtime in
that case.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88758
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Michel Dänzer <michel.daenzer@xxxxxxx>
Interesting I wonder what the rational behind this is. I mean
CONFIG_X86_PAT will obviously affect write combining, but why does it
slow down things if we request something that the kernel isn't
configured for?
Anyway, patch is Reviewed-by: Christian König <christian.koenig@xxxxxxx>
Regards,
Christian.
---
drivers/gpu/drm/radeon/radeon_object.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/drivers/gpu/drm/radeon/radeon_object.c b/drivers/gpu/drm/radeon/radeon_object.c
index 7d68223..bd3df10 100644
--- a/drivers/gpu/drm/radeon/radeon_object.c
+++ b/drivers/gpu/drm/radeon/radeon_object.c
@@ -238,6 +238,18 @@ int radeon_bo_create(struct radeon_device *rdev,
* See https://bugs.freedesktop.org/show_bug.cgi?id=84627
*/
bo->flags &= ~RADEON_GEM_GTT_WC;
+#elif defined(CONFIG_X86) && !defined(CONFIG_X86_PAT)
+ /* Don't try to enable write-combining when it can't work, or things
+ * may be slow
+ * See https://bugs.freedesktop.org/show_bug.cgi?id=88758
+ */
+
+#warning Please enable CONFIG_MTRR and CONFIG_X86_PAT for better performance \
+ thanks to write-combining
+
+ DRM_INFO_ONCE("Please enable CONFIG_MTRR and CONFIG_X86_PAT for "
+ "better performance thanks to write-combining\n");
+ bo->flags &= ~RADEON_GEM_GTT_WC;
#endif
radeon_ttm_placement_from_domain(bo, domain);
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