thunderbolt: Add DP IN resources for all routers

USB4 spec allows DP tunneling from any router that has DP IN adapter,
not just from host router. The driver currently only added the DP IN
resources for the host router because Thunderbolt 1, 2 and 3 devices do
not have DP IN adapters. However, USB4 allows device routers to have DP
IN adapter as well so update the driver to add DP IN resources for each
device that has one. One example would be an eGPU enclosure where the
eGPU output is forwarded to DP IN port and then tunneled over the USB4
fabric.

Only limitation we add now is that the DP IN and DP OUT that gets paired
for tunnel creation should both be under the same topology starting from
host router downstream port. In other words we do not create DP tunnels
across host router at this time even though that is possible as well but
it complicates the bandwidth management and there is no real use-case
for this anyway.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/tb.c

@@ -404,6 +404,7 @@ static void tb_scan_port(struct tb_port *port)
 	if (tcm->hotplug_active && tb_tunnel_usb3(sw->tb, sw))
 		tb_sw_warn(sw, "USB3 tunnel creation failed\n");
 
+	tb_add_dp_resources(sw);
 	tb_scan_switch(sw);
 }
 
@@ -573,6 +574,43 @@ static int tb_available_bw(struct tb_cm *tcm, struct tb_port *in,
 	return available_bw;
 }
 
+static struct tb_port *tb_find_dp_out(struct tb *tb, struct tb_port *in)
+{
+	struct tb_port *host_port, *port;
+	struct tb_cm *tcm = tb_priv(tb);
+
+	host_port = tb_route(in->sw) ?
+		tb_port_at(tb_route(in->sw), tb->root_switch) : NULL;
+
+	list_for_each_entry(port, &tcm->dp_resources, list) {
+		if (!tb_port_is_dpout(port))
+			continue;
+
+		if (tb_port_is_enabled(port)) {
+			tb_port_dbg(port, "in use\n");
+			continue;
+		}
+
+		tb_port_dbg(port, "DP OUT available\n");
+
+		/*
+		 * Keep the DP tunnel under the topology starting from
+		 * the same host router downstream port.
+		 */
+		if (host_port && tb_route(port->sw)) {
+			struct tb_port *p;
+
+			p = tb_port_at(tb_route(port->sw), tb->root_switch);
+			if (p != host_port)
+				continue;
+		}
+
+		return port;
+	}
+
+	return NULL;
+}
+
 static void tb_tunnel_dp(struct tb *tb)
 {
 	struct tb_cm *tcm = tb_priv(tb);
@@ -589,17 +627,21 @@ static void tb_tunnel_dp(struct tb *tb)
 	in = NULL;
 	out = NULL;
 	list_for_each_entry(port, &tcm->dp_resources, list) {
+		if (!tb_port_is_dpin(port))
+			continue;
+
 		if (tb_port_is_enabled(port)) {
 			tb_port_dbg(port, "in use\n");
 			continue;
 		}
 
-		tb_port_dbg(port, "available\n");
+		tb_port_dbg(port, "DP IN available\n");
 
-		if (!in && tb_port_is_dpin(port))
+		out = tb_find_dp_out(tb, port);
+		if (out) {
 			in = port;
-		else if (!out && tb_port_is_dpout(port))
-			out = port;
+			break;
+		}
 	}
 
 	if (!in) {