thunderbolt: Add default linking between lane adapters if not provided by DROM

We currently read how sibling lane adapter ports relate each other from
DROM (Device ROM). If the two lane adapter ports go through the same
physical connector these lanes can then be bonded together. However,
some cases DROM does not provide this information or it is missing
completely (host routers typically do not have DROM). In this case we
have hard-coded the relationship.

Expand this to work with both legacy devices where lane adapter ports 1
and 2, and 3 and 4 are always linked together, and with USB4 devices
where lane adapter 1 is always following lane adapter 0 or is disabled
completely (see USB4 section 5.2.1 for more information).
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/eeprom.c

@@ -514,17 +514,6 @@ int tb_drom_read(struct tb_switch *sw)
 		 * no entries). Hardcode the configuration here.
 		 */
 		tb_drom_read_uid_only(sw, &sw->uid);
-
-		sw->ports[1].link_nr = 0;
-		sw->ports[2].link_nr = 1;
-		sw->ports[1].dual_link_port = &sw->ports[2];
-		sw->ports[2].dual_link_port = &sw->ports[1];
-
-		sw->ports[3].link_nr = 0;
-		sw->ports[4].link_nr = 1;
-		sw->ports[3].dual_link_port = &sw->ports[4];
-		sw->ports[4].dual_link_port = &sw->ports[3];
-
 		return 0;
 	}
 

drivers/thunderbolt/switch.c

@@ -1936,6 +1936,36 @@ static int tb_switch_add_dma_port(struct tb_switch *sw)
 	return -ESHUTDOWN;
 }
 
+static void tb_switch_default_link_ports(struct tb_switch *sw)
+{
+	int i;
+
+	for (i = 1; i <= sw->config.max_port_number; i += 2) {
+		struct tb_port *port = &sw->ports[i];
+		struct tb_port *subordinate;
+
+		if (!tb_port_is_null(port))
+			continue;
+
+		/* Check for the subordinate port */
+		if (i == sw->config.max_port_number ||
+		    !tb_port_is_null(&sw->ports[i + 1]))
+			continue;
+
+		/* Link them if not already done so (by DROM) */
+		subordinate = &sw->ports[i + 1];
+		if (!port->dual_link_port && !subordinate->dual_link_port) {
+			port->link_nr = 0;
+			port->dual_link_port = subordinate;
+			subordinate->link_nr = 1;
+			subordinate->dual_link_port = port;
+
+			tb_sw_dbg(sw, "linked ports %d <-> %d\n",
+				  port->port, subordinate->port);
+		}
+	}
+}
+
 static bool tb_switch_lane_bonding_possible(struct tb_switch *sw)
 {
 	const struct tb_port *up = tb_upstream_port(sw);
@@ -2109,6 +2139,8 @@ int tb_switch_add(struct tb_switch *sw)
 			}
 		}
 
+		tb_switch_default_link_ports(sw);
+
 		ret = tb_switch_update_link_attributes(sw);
 		if (ret)
 			return ret;