net: dsa: add port fast ageing

Today the DSA drivers are in charge of flushing the MAC addresses
associated to a port when its STP state changes from Learning or
Forwarding, to Disabled or Blocking or Listening.

This makes the drivers more complex and hides the generic switch logic.
Introduce a new optional port_fast_age operation to dsa_switch_ops, to
move this logic to the DSA layer and keep drivers simple.
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dsa.h

@@ -143,6 +143,7 @@ struct dsa_port {
 	struct net_device	*netdev;
 	struct device_node	*dn;
 	unsigned int		ageing_time;
+	u8			stp_state;
 };
 
 struct dsa_switch {
@@ -339,6 +340,7 @@ struct dsa_switch_ops {
 	void	(*port_bridge_leave)(struct dsa_switch *ds, int port);
 	void	(*port_stp_state_set)(struct dsa_switch *ds, int port,
 				      u8 state);
+	void	(*port_fast_age)(struct dsa_switch *ds, int port);
 
 	/*
 	 * VLAN support

net/dsa/slave.c

@@ -71,8 +71,26 @@ static inline bool dsa_port_is_bridged(struct dsa_slave_priv *p)
 
 static void dsa_port_set_stp_state(struct dsa_switch *ds, int port, u8 state)
 {
+	struct dsa_port *dp = &ds->ports[port];
+
 	if (ds->ops->port_stp_state_set)
 		ds->ops->port_stp_state_set(ds, port, state);
+
+	if (ds->ops->port_fast_age) {
+		/* Fast age FDB entries or flush appropriate forwarding database
+		 * for the given port, if we are moving it from Learning or
+		 * Forwarding state, to Disabled or Blocking or Listening state.
+		 */
+
+		if ((dp->stp_state == BR_STATE_LEARNING ||
+		     dp->stp_state == BR_STATE_FORWARDING) &&
+		    (state == BR_STATE_DISABLED ||
+		     state == BR_STATE_BLOCKING ||
+		     state == BR_STATE_LISTENING))
+			ds->ops->port_fast_age(ds, port);
+	}
+
+	dp->stp_state = state;
 }
 
 static int dsa_slave_open(struct net_device *dev)