drm/dp_mst: Remove PDT teardown in drm_dp_destroy_port() and refactor

This will allow us to add some locking for port->* members, in
particular the PDT and ->connector, which can't be done from
drm_dp_destroy_port() since we don't know what locks the caller might be
holding.

Note that we already do this in delayed_destroy_work (renamed from
destroy_connector_work in this patch) for ports, we're just making it so
mstbs are also destroyed in this worker.

Changes since v2:
* Clarify commit message
Changes since v4:
* Clarify commit message more

Cc: Juston Li <juston.li@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191022023641.8026-3-lyude@redhat.com

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -1510,31 +1510,22 @@ static void drm_dp_destroy_port(struct kref *kref)
 		container_of(kref, struct drm_dp_mst_port, topology_kref);
 	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
 
-	if (!port->input) {
+	/* There's nothing that needs locking to destroy an input port yet */
+	if (port->input) {
+		drm_dp_mst_put_port_malloc(port);
+		return;
+	}
+
 	kfree(port->cached_edid);
 
 	/*
-		 * The only time we don't have a connector
-		 * on an output port is if the connector init
-		 * fails.
+	 * we can't destroy the connector here, as we might be holding the
+	 * mode_config.mutex from an EDID retrieval
 	 */
-		if (port->connector) {
-			/* we can't destroy the connector here, as
-			 * we might be holding the mode_config.mutex
-			 * from an EDID retrieval */
-
 	mutex_lock(&mgr->delayed_destroy_lock);
 	list_add(&port->next, &mgr->destroy_port_list);
 	mutex_unlock(&mgr->delayed_destroy_lock);
 	schedule_work(&mgr->delayed_destroy_work);
-			return;
-		}
-		/* no need to clean up vcpi
-		 * as if we have no connector we never setup a vcpi */
-		drm_dp_port_teardown_pdt(port, port->pdt);
-		port->pdt = DP_PEER_DEVICE_NONE;
-	}
-	drm_dp_mst_put_port_malloc(port);
 }
 
 /**
@@ -3981,6 +3972,7 @@ static void drm_dp_tx_work(struct work_struct *work)
 static inline void
 drm_dp_delayed_destroy_port(struct drm_dp_mst_port *port)
 {
+	if (port->connector)
 		port->mgr->cbs->destroy_connector(port->mgr, port->connector);
 
 	drm_dp_port_teardown_pdt(port, port->pdt);