net: dsa: Add helper for converting devlink port to ds and port

Hide away from DSA drivers how devlink works.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dsa.h

@@ -701,6 +701,20 @@ static inline struct dsa_switch *dsa_devlink_to_ds(struct devlink *dl)
 	return dl_priv->ds;
 }
 
+static inline
+struct dsa_switch *dsa_devlink_port_to_ds(struct devlink_port *port)
+{
+	struct devlink *dl = port->devlink;
+	struct dsa_devlink_priv *dl_priv = devlink_priv(dl);
+
+	return dl_priv->ds;
+}
+
+static inline int dsa_devlink_port_to_port(struct devlink_port *port)
+{
+	return port->index;
+}
+
 struct dsa_switch_driver {
 	struct list_head	list;
 	const struct dsa_switch_ops *ops;