thunderbolt: Allow USB3 bandwidth to be lower than maximum supported

Currently USB3 tunnel setup fails if USB4 link available bandwidth is too low
to allow USB3 Maximum Supported Link Rate. In reality, this limitation is not
needed, and may cause failure of USB3 tunnel establishment, if USB4 link
available bandwidth is lower than USB3 Maximum Supported Link Rate. E.g. if we
connect to USB4 v1 host router, a USB4 v1 device router, via 10 Gb/s cable.
Hence, here we discard this limitation, and now we only limit USB3 bandwidth
allocation to be not higher than 90% of USB3 Max Supported Link Rate (for first
USB3 tunnel only).

Signed-off-by: Gil Fine <[email protected]>
Signed-off-by: Mika Westerberg <[email protected]>

Author: Gil Fine

drivers/thunderbolt/tunnel.c

@@ -2064,26 +2064,21 @@ struct tb_tunnel *tb_tunnel_alloc_usb3(struct tb *tb, struct tb_port *up,
 {
 	struct tb_tunnel *tunnel;
 	struct tb_path *path;
-	int max_rate = 0;
+	int max_rate;
 
-	/*
-	 * Check that we have enough bandwidth available for the new
-	 * USB3 tunnel.
-	 */
-	if (max_up > 0 || max_down > 0) {
+	if (!tb_route(down->sw) && (max_up > 0 || max_down > 0)) {
+		/*
+		 * For USB3 isochronous transfers, we allow bandwidth which is
+		 * not higher than 90% of maximum supported bandwidth by USB3
+		 * adapters.
+		 */
 		max_rate = tb_usb3_max_link_rate(down, up);
 		if (max_rate < 0)
 			return NULL;
 
-		/* Only 90% can be allocated for USB3 isochronous transfers */
 		max_rate = max_rate * 90 / 100;
-		tb_port_dbg(up, "required bandwidth for USB3 tunnel %d Mb/s\n",
+		tb_port_dbg(up, "maximum required bandwidth for USB3 tunnel %d Mb/s\n",
 			    max_rate);
-
-		if (max_rate > max_up || max_rate > max_down) {
-			tb_port_warn(up, "not enough bandwidth for USB3 tunnel\n");
-			return NULL;
-		}
 	}
 
 	tunnel = tb_tunnel_alloc(tb, 2, TB_TUNNEL_USB3);
@@ -2115,8 +2110,8 @@ struct tb_tunnel *tb_tunnel_alloc_usb3(struct tb *tb, struct tb_port *up,
 	tunnel->paths[TB_USB3_PATH_UP] = path;
 
 	if (!tb_route(down->sw)) {
-		tunnel->allocated_up = max_rate;
-		tunnel->allocated_down = max_rate;
+		tunnel->allocated_up = min(max_rate, max_up);
+		tunnel->allocated_down = min(max_rate, max_down);
 
 		tunnel->init = tb_usb3_init;
 		tunnel->consumed_bandwidth = tb_usb3_consumed_bandwidth;