net: dsa: Do not register devlink for unused ports

Even if commit 1d27732f411d ("net: dsa: setup and teardown ports") indicated
that registering a devlink instance for unused ports is not a problem, and this
is true, this can be confusing nonetheless, so let's not do it.

Fixes: 1d27732f411d ("net: dsa: setup and teardown ports")
Reported-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/dsa2.c

@@ -258,11 +258,13 @@ static void dsa_tree_teardown_default_cpu(struct dsa_switch_tree *dst)
 static int dsa_port_setup(struct dsa_port *dp)
 {
 	struct dsa_switch *ds = dp->ds;
-	int err;
+	int err = 0;
 
 	memset(&dp->devlink_port, 0, sizeof(dp->devlink_port));
 
-	err = devlink_port_register(ds->devlink, &dp->devlink_port, dp->index);
+	if (dp->type != DSA_PORT_TYPE_UNUSED)
+		err = devlink_port_register(ds->devlink, &dp->devlink_port,
+					    dp->index);
 	if (err)
 		return err;
 
@@ -293,7 +295,8 @@ static int dsa_port_setup(struct dsa_port *dp)
 
 static void dsa_port_teardown(struct dsa_port *dp)
 {
-	devlink_port_unregister(&dp->devlink_port);
+	if (dp->type != DSA_PORT_TYPE_UNUSED)
+		devlink_port_unregister(&dp->devlink_port);
 
 	switch (dp->type) {
 	case DSA_PORT_TYPE_UNUSED: