net: dsa: refactor the prechangeupper sanity checks into a dedicated function

We need to add more logic to the DSA NETDEV_PRECHANGEUPPER event
handler, more exactly we need to request an unsync of switchdev objects.
In order to fit more code, refactor the existing logic into a helper.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/slave.c

@@ -2166,20 +2166,16 @@ dsa_slave_check_8021q_upper(struct net_device *dev,
 	return NOTIFY_DONE;
 }
 
-static int dsa_slave_netdevice_event(struct notifier_block *nb,
-				     unsigned long event, void *ptr)
+static int
+dsa_slave_prechangeupper_sanity_check(struct net_device *dev,
+				      struct netdev_notifier_changeupper_info *info)
 {
-	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
-
-	switch (event) {
-	case NETDEV_PRECHANGEUPPER: {
-		struct netdev_notifier_changeupper_info *info = ptr;
 	struct dsa_switch *ds;
 	struct dsa_port *dp;
 	int err;
 
 	if (!dsa_slave_dev_check(dev))
-			return dsa_prevent_bridging_8021q_upper(dev, ptr);
+		return dsa_prevent_bridging_8021q_upper(dev, info);
 
 	dp = dsa_slave_to_port(dev);
 	ds = dp->ds;
@@ -2191,7 +2187,25 @@ static int dsa_slave_netdevice_event(struct notifier_block *nb,
 	}
 
 	if (is_vlan_dev(info->upper_dev))
-			return dsa_slave_check_8021q_upper(dev, ptr);
+		return dsa_slave_check_8021q_upper(dev, info);
+
+	return NOTIFY_DONE;
+}
+
+static int dsa_slave_netdevice_event(struct notifier_block *nb,
+				     unsigned long event, void *ptr)
+{
+	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
+
+	switch (event) {
+	case NETDEV_PRECHANGEUPPER: {
+		struct netdev_notifier_changeupper_info *info = ptr;
+		int err;
+
+		err = dsa_slave_prechangeupper_sanity_check(dev, info);
+		if (err != NOTIFY_DONE)
+			return err;
+
 		break;
 	}
 	case NETDEV_CHANGEUPPER: