net: dsa: notify drivers of MAC address changes on user ports

In some cases, drivers may need to veto the changing of a MAC address on
a user port. Such is the case with KSZ9477 when it offloads a HSR device,
because it programs the MAC address of multiple ports to a shared
hardware register. Those ports need to have equal MAC addresses for the
lifetime of the HSR offload.

Signed-off-by: Vladimir Oltean <[e-mail]>
Signed-off-by: Lukasz Majewski <[e-mail]>
Reviewed-by: Florian Fainelli <[e-mail]>
Reviewed-by: Vladimir Oltean <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

include/net/dsa.h

···
 			       struct phy_device *phy);
 	void	(*port_disable)(struct dsa_switch *ds, int port);
 
+
+	/*
+	 * Notification for MAC address changes on user ports. Drivers can
+	 * currently only veto operations. They should not use the method to
+	 * program the hardware, since the operation is not rolled back in case
+	 * of other errors.
+	 */
+	int	(*port_set_mac_address)(struct dsa_switch *ds, int port,
+					const unsigned char *addr);
+
 	/*
 	 * Compatibility between device trees defining multiple CPU ports and
 	 * drivers which are not OK to use by default the numerically smallest

net/dsa/slave.c

···
 	if (!is_valid_ether_addr(addr->sa_data))
 		return -EADDRNOTAVAIL;
 
+	if (ds->ops->port_set_mac_address) {
+		err = ds->ops->port_set_mac_address(ds, dp->index,
+						    addr->sa_data);
+		if (err)
+			return err;
+	}
+
 	/* If the port is down, the address isn't synced yet to hardware or
 	 * to the DSA master, so there is nothing to change.
 	 */