i915: wait for fence in prepare_plane_fb

In intel_prepare_plane_fb, if fb is backed by dma-buf, wait for exclusive
fence

v2: First commit
v3: Remove object_name_lock acquire
    Move wait from intel_atomic_commit() to intel_prepare_plane_fb()
v4: Wait only on exclusive fences, interruptible with no timeout
v5: Style tweaks to more closely match rest of file
v6: Properly handle interrupted waits
v7: No change
v8: No change

Link: https://patchwork.kernel.org/patch/7704181/
Signed-off-by: Alex Goins <agoins@nvidia.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -13690,6 +13690,17 @@ intel_prepare_plane_fb(struct drm_plane *plane,
 			return ret;
 	}
 
+	/* For framebuffer backed by dmabuf, wait for fence */
+	if (obj && obj->base.dma_buf) {
+		ret = reservation_object_wait_timeout_rcu(obj->base.dma_buf->resv,
+							  false, true,
+							  MAX_SCHEDULE_TIMEOUT);
+		if (ret == -ERESTARTSYS)
+			return ret;
+
+		WARN_ON(ret < 0);
+	}
+
 	if (!obj) {
 		ret = 0;
 	} else if (plane->type == DRM_PLANE_TYPE_CURSOR &&