thunderbolt: Scan retimers after device router has been enumerated

Thomas reported connection issues on AMD system with Pluggable UD-4VPD
dock. After some experiments it looks like the device has some sort of
internal timeout that triggers reconnect. This is completely against the
USB4 spec, as there is no requirement for the host to enumerate the
device right away or even at all.

In Linux case the delay is caused by scanning of retimers on the link so
we can work this around by doing the scanning after the device router
has been enumerated.

Reported-by: Thomas Lynema <lyz27@yahoo.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219748
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

Author: westeri

drivers/thunderbolt/tb.c

@@ -1305,11 +1305,15 @@ static void tb_scan_port(struct tb_port *port)
 		goto out_rpm_put;
 	}
 
-	tb_retimer_scan(port, true);
-
 	sw = tb_switch_alloc(port->sw->tb, &port->sw->dev,
 			     tb_downstream_route(port));
 	if (IS_ERR(sw)) {
+		/*
+		 * Make the downstream retimers available even if there
+		 * is no router connected.
+		 */
+		tb_retimer_scan(port, true);
+
 		/*
 		 * If there is an error accessing the connected switch
 		 * it may be connected to another domain. Also we allow
@@ -1359,6 +1363,14 @@ static void tb_scan_port(struct tb_port *port)
 	upstream_port = tb_upstream_port(sw);
 	tb_configure_link(port, upstream_port, sw);
 
+	/*
+	 * Scan for downstream retimers. We only scan them after the
+	 * router has been enumerated to avoid issues with certain
+	 * Pluggable devices that expect the host to enumerate them
+	 * within certain timeout.
+	 */
+	tb_retimer_scan(port, true);
+
 	/*
 	 * CL0s and CL1 are enabled and supported together.
 	 * Silently ignore CLx enabling in case CLx is not supported.