Re: [PATCH] drm/radeon: Don't try to enable write-combining without PAT

On Wed, Feb 4, 2015 at 4:49 AM, Christian König deathsimple@vodafone.de wrote:

Am 04.02.2015 um 02:19 schrieb Michel Dänzer:

...

From: Michel Dänzer michel.daenzer@amd.com

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@vger.kernel.org Signed-off-by: Michel Dänzer michel.daenzer@amd.com

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@amd.com

Applied to my 3.20 tree.

Thanks!

Alex

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);

---

dri-devel mailing list dri-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/dri-devel