drm/amdgpu: Fix hard hang for S/G display BOs.

HW requires for caching to be unset for scanout BO
mappings when the BO placement is in GTT memory.
Usually the flag to unset is passed from user mode
but for FB mode this was missing.

v2:
Keep all BO placement logic in amdgpu_display_supported_domains
Suggested-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Tested-by: Shirish S <shirish.s@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -139,14 +139,14 @@ static int amdgpufb_create_pinned_object(struct amdgpu_fbdev *rfbdev,
 	mode_cmd->pitches[0] = amdgpu_align_pitch(adev, mode_cmd->width, cpp,
 						  fb_tiled);
 	domain = amdgpu_display_supported_domains(adev);
-
 	height = ALIGN(mode_cmd->height, 8);
 	size = mode_cmd->pitches[0] * height;
 	aligned_size = ALIGN(size, PAGE_SIZE);
 	ret = amdgpu_gem_object_create(adev, aligned_size, 0, domain,
 				       AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED |
-				       AMDGPU_GEM_CREATE_VRAM_CONTIGUOUS |
-				       AMDGPU_GEM_CREATE_VRAM_CLEARED,
+				       AMDGPU_GEM_CREATE_VRAM_CONTIGUOUS     |
+				       AMDGPU_GEM_CREATE_VRAM_CLEARED 	     |
+				       AMDGPU_GEM_CREATE_CPU_GTT_USWC,
 				       ttm_bo_type_kernel, NULL, &gobj);
 	if (ret) {
 		pr_err("failed to allocate framebuffer (%d)\n", aligned_size);
@@ -168,7 +168,6 @@ static int amdgpufb_create_pinned_object(struct amdgpu_fbdev *rfbdev,
 			dev_err(adev->dev, "FB failed to set tiling flags\n");
 	}
 
-
 	ret = amdgpu_bo_pin(abo, domain);
 	if (ret) {
 		amdgpu_bo_unreserve(abo);

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

@@ -747,7 +747,8 @@ int amdgpu_mode_dumb_create(struct drm_file *file_priv,
 	struct amdgpu_device *adev = dev->dev_private;
 	struct drm_gem_object *gobj;
 	uint32_t handle;
-	u64 flags = AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED;
+	u64 flags = AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED |
+		    AMDGPU_GEM_CREATE_CPU_GTT_USWC;
 	u32 domain;
 	int r;