drm/i915/overlay: Ensure that the reg_bo is in the GTT prior to writing.

Just makes sure that writes are not being aliased by the CPU cache and
do make it out to main memory.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=24977
Cc: stable@kernel.org

drivers/gpu/drm/i915/intel_overlay.c

@@ -1386,6 +1386,12 @@ void intel_setup_overlay(struct drm_device *dev)
                         goto out_free_bo;
                 }
 		overlay->flip_addr = overlay->reg_bo->gtt_offset;
+
+		ret = i915_gem_object_set_to_gtt_domain(reg_bo, true);
+		if (ret) {
+                        DRM_ERROR("failed to move overlay register bo into the GTT\n");
+                        goto out_unpin_bo;
+                }
 	} else {
 		ret = i915_gem_attach_phys_object(dev, reg_bo,
 						  I915_GEM_PHYS_OVERLAY_REGS,
@@ -1418,6 +1424,8 @@ void intel_setup_overlay(struct drm_device *dev)
 	DRM_INFO("initialized overlay support\n");
 	return;
 
+out_unpin_bo:
+	i915_gem_object_unpin(reg_bo);
 out_free_bo:
 	drm_gem_object_unreference(reg_bo);
 out_free: