thunderbolt: Fix minimum allocated USB 3.x and PCIe bandwidth

With the current bandwidth allocation we end up reserving too much for the USB
3.x and PCIe tunnels that leads to reduced capabilities for the second
DisplayPort tunnel.

Fix this by decreasing the USB 3.x allocation to 900 Mb/s which then allows
both tunnels to get the maximum HBR2 bandwidth.  This way, the reserved
bandwidth for USB 3.x and PCIe, would be 1350 Mb/s (taking weights of USB 3.x
and PCIe into account). So bandwidth allocations on a link are:
USB 3.x + PCIe tunnels => 1350 Mb/s
DisplayPort tunnel #1  => 17280 Mb/s
DisplayPort tunnel #2  => 17280 Mb/s

Total consumed bandwidth is 35910 Mb/s. So that all the above can be tunneled
on a Gen 3 link (which allows maximum of 36000 Mb/s).

Fixes: 582e70b ("thunderbolt: Change bandwidth reservations to comply USB4 v2")
Signed-off-by: Gil Fine <[email protected]>
Signed-off-by: Mika Westerberg <[email protected]>

drivers/thunderbolt/usb4.c

@@ -2311,13 +2311,13 @@ int usb4_usb3_port_release_bandwidth(struct tb_port *port, int *upstream_bw,
 		goto err_request;
 
 	/*
-	 * Always keep 1000 Mb/s to make sure xHCI has at least some
+	 * Always keep 900 Mb/s to make sure xHCI has at least some
 	 * bandwidth available for isochronous traffic.
 	 */
-	if (consumed_up < 1000)
-		consumed_up = 1000;
-	if (consumed_down < 1000)
-		consumed_down = 1000;
+	if (consumed_up < 900)
+		consumed_up = 900;
+	if (consumed_down < 900)
+		consumed_down = 900;
 
 	ret = usb4_usb3_port_write_allocated_bandwidth(port, consumed_up,
 						       consumed_down);