thunderbolt: Do not create DisplayPort tunnels on adapters of the same router

commit c032cdd48b upstream.

Probably due to a firmware bug Dell TB16 dock announces that one of its
DisplayPort adapters is actually DP IN. Now this is possible and used
with some external GPUs but not likely in this case as we are dealing
with a dock. Anyways the problem is that the driver tries to create a
DisplayPort tunnel between adapters of the same router which then shows
to user that there is no picture on the display (because there are no
available DP OUT adapters on the dock anymore).

Fix this by not creating DisplayPort tunnels between adapters that are
on the same router.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/10265
Fixes: 274baf695b ("thunderbolt: Add DP IN added last in the head of the list of DP resources")
Cc: Gil Fine <gil.fine@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/thunderbolt/tb.c

@@ -1717,6 +1717,12 @@ static struct tb_port *tb_find_dp_out(struct tb *tb, struct tb_port *in)
 			continue;
 		}
 
+		/* Needs to be on different routers */
+		if (in->sw == port->sw) {
+			tb_port_dbg(port, "skipping DP OUT on same router\n");
+			continue;
+		}
+
 		tb_port_dbg(port, "DP OUT available\n");
 
 		/*