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

BugLink: http://bugs.launchpad.net/bugs/1546572Reviewed-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>
Cc: stable@vger.kernel.org
(cherry picked from commit a187f17f)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_object.c

@@ -33,6 +33,7 @@
 #include <linux/slab.h>
 #include <drm/drmP.h>
 #include <drm/amdgpu_drm.h>
+#include <drm/drm_cache.h>
 #include "amdgpu.h"
 #include "amdgpu_trace.h"
 
@@ -261,6 +262,13 @@ int amdgpu_bo_create_restricted(struct amdgpu_device *adev,
 				       AMDGPU_GEM_DOMAIN_OA);
 
 	bo->flags = flags;
+
+	/* For architectures that don't support WC memory,
+	 * mask out the WC flag from the BO
+	 */
+	if (!drm_arch_can_wc_memory())
+		bo->flags &= ~AMDGPU_GEM_CREATE_CPU_GTT_USWC;
+
 	amdgpu_fill_placement_to_bo(bo, placement);
 	/* Kernel allocation are uninterruptible */
 	r = ttm_bo_init(&adev->mman.bdev, &bo->tbo, size, type,