drm/i915: Take all modeset locks for DP MST hotplug

While auditing various users of the connector/encoder lists I realized
that the atomic code is a very prolific user of them. And it only ever
grabs the mode_config->connection_mutex, but not the
mode_config->mutex like all the other code walking encoder/connector
lists.

The problem is that we can't grab the mode_config.mutex late in atomic
code since that would lead to locking inversions. And we don't want to
grab it unconditionally like the legacy set_config modeset path since
that would render all the fine-grained locking moot.

Instead just grab more locks in the dp mst hotplug code. Note that
drm_connector_init (which is the one adding the connector to these
lists) already uses drm_modeset_lock_all.

The other reason for grabbing all locks is that the dpms off in the
unplug function amounts to a modeset, so better to take all required
locks for that.
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/i915/intel_dp_mst.c

@@ -442,9 +442,9 @@ static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topolo
 
 	drm_mode_connector_set_path_property(connector, pathprop);
 	drm_reinit_primary_mode_group(dev);
-	mutex_lock(&dev->mode_config.mutex);
+	drm_modeset_lock_all(dev);
 	intel_connector_add_to_fbdev(intel_connector);
-	mutex_unlock(&dev->mode_config.mutex);
+	drm_modeset_unlock_all(dev);
 	drm_connector_register(&intel_connector->base);
 	return connector;
 }
@@ -455,16 +455,16 @@ static void intel_dp_destroy_mst_connector(struct drm_dp_mst_topology_mgr *mgr,
 	struct intel_connector *intel_connector = to_intel_connector(connector);
 	struct drm_device *dev = connector->dev;
 	/* need to nuke the connector */
-	mutex_lock(&dev->mode_config.mutex);
+	drm_modeset_lock_all(dev);
 	intel_connector_dpms(connector, DRM_MODE_DPMS_OFF);
-	mutex_unlock(&dev->mode_config.mutex);
+	drm_modeset_unlock_all(dev);
 
 	intel_connector->unregister(intel_connector);
 
-	mutex_lock(&dev->mode_config.mutex);
+	drm_modeset_lock_all(dev);
 	intel_connector_remove_from_fbdev(intel_connector);
 	drm_connector_cleanup(connector);
-	mutex_unlock(&dev->mode_config.mutex);
+	drm_modeset_unlock_all(dev);
 
 	drm_reinit_primary_mode_group(dev);