drm/display/dp_mst: Drop all ports from topology on CSNs before queueing link address work

We want to start cutting down on all of the places that we use port
validation, so that ports may be removed from the topology as quickly as
possible to minimize the number of errors we run into as a result of being
out of sync with the current topology status. This isn't a very typical
scenario and I don't think I've ever even run into it - but since the next
commit is going to make some changes to payload updates depending on their
hotplug status I think it's a probably good idea to take precautions.

Let's do this with CSNs by moving some code around so that we only queue
link address probing work at the end of handling all CSNs - allowing us to
make sure we drop as many topology references as we can beforehand.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Wayne Lin <Wayne.Lin@amd.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Fangzhi Zuo <Jerry.Zuo@amd.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sean Paul <sean@poorly.run>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220817193847.557945-15-lyude@redhat.com

drivers/gpu/drm/display/drm_dp_mst_topology.c

@@ -2509,7 +2509,7 @@ drm_dp_mst_handle_link_address_port(struct drm_dp_mst_branch *mstb,
 	return ret;
 }
 
-static void
+static int
 drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
 			    struct drm_dp_connection_status_notify *conn_stat)
 {
@@ -2522,7 +2522,7 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
 
 	port = drm_dp_get_port(mstb, conn_stat->port_number);
 	if (!port)
-		return;
+		return 0;
 
 	if (port->connector) {
 		if (!port->input && conn_stat->input_port) {
@@ -2575,8 +2575,7 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
 
 out:
 	drm_dp_mst_topology_put_port(port);
-	if (dowork)
-		queue_work(system_long_wq, &mstb->mgr->work);
+	return dowork;
 }
 
 static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_topology_mgr *mgr,
@@ -4060,7 +4059,7 @@ drm_dp_mst_process_up_req(struct drm_dp_mst_topology_mgr *mgr,
 	struct drm_dp_mst_branch *mstb = NULL;
 	struct drm_dp_sideband_msg_req_body *msg = &up_req->msg;
 	struct drm_dp_sideband_msg_hdr *hdr = &up_req->hdr;
-	bool hotplug = false;
+	bool hotplug = false, dowork = false;
 
 	if (hdr->broadcast) {
 		const u8 *guid = NULL;
@@ -4083,11 +4082,14 @@ drm_dp_mst_process_up_req(struct drm_dp_mst_topology_mgr *mgr,
 
 	/* TODO: Add missing handler for DP_RESOURCE_STATUS_NOTIFY events */
 	if (msg->req_type == DP_CONNECTION_STATUS_NOTIFY) {
-		drm_dp_mst_handle_conn_stat(mstb, &msg->u.conn_stat);
+		dowork = drm_dp_mst_handle_conn_stat(mstb, &msg->u.conn_stat);
 		hotplug = true;
 	}
 
 	drm_dp_mst_topology_put_mstb(mstb);
+
+	if (dowork)
+		queue_work(system_long_wq, &mgr->work);
 	return hotplug;
 }