drm/radeon: mask out WC from BO on unsupported arches

BugLink: http://bugs.launchpad.net/bugs/1553179

commit c5244987 upstream.
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/gpu/drm/radeon/radeon_object.c

@@ -33,6 +33,7 @@
 #include <linux/slab.h>
 #include <drm/drmP.h>
 #include <drm/radeon_drm.h>
+#include <drm/drm_cache.h>
 #include "radeon.h"
 #include "radeon_trace.h"
 
@@ -245,6 +246,12 @@ int radeon_bo_create(struct radeon_device *rdev,
 		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 | RADEON_GEM_GTT_UC);
+#else
+	/* For architectures that don't support WC memory,
+	 * mask out the WC flag from the BO
+	 */
+	if (!drm_arch_can_wc_memory())
+		bo->flags &= ~RADEON_GEM_GTT_WC;
 #endif
 
 	radeon_ttm_placement_from_domain(bo, domain);