net: dsa: add slave to port helper

Many portions of DSA core code require to get the dsa_port structure
corresponding to a slave net_device. For this purpose, introduce a
dsa_slave_to_port() helper.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/dsa_priv.h

@@ -169,6 +169,13 @@ int dsa_slave_resume(struct net_device *slave_dev);
 int dsa_slave_register_notifier(void);
 void dsa_slave_unregister_notifier(void);
 
+static inline struct dsa_port *dsa_slave_to_port(const struct net_device *dev)
+{
+	struct dsa_slave_priv *p = netdev_priv(dev);
+
+	return p->dp;
+}
+
 /* switch.c */
 int dsa_switch_register_notifier(struct dsa_switch *ds);
 void dsa_switch_unregister_notifier(struct dsa_switch *ds);

net/dsa/legacy.c

@@ -740,8 +740,7 @@ int dsa_legacy_fdb_add(struct ndmsg *ndm, struct nlattr *tb[],
 		       const unsigned char *addr, u16 vid,
 		       u16 flags)
 {
-	struct dsa_slave_priv *p = netdev_priv(dev);
-	struct dsa_port *dp = p->dp;
+	struct dsa_port *dp = dsa_slave_to_port(dev);
 
 	return dsa_port_fdb_add(dp, addr, vid);
 }
@@ -750,8 +749,7 @@ int dsa_legacy_fdb_del(struct ndmsg *ndm, struct nlattr *tb[],
 		       struct net_device *dev,
 		       const unsigned char *addr, u16 vid)
 {
-	struct dsa_slave_priv *p = netdev_priv(dev);
-	struct dsa_port *dp = p->dp;
+	struct dsa_port *dp = dsa_slave_to_port(dev);
 
 	return dsa_port_fdb_del(dp, addr, vid);
 }