net: dsa: mv88e6xxx: share the same default FDB

For hardware cross-chip bridging to work, user ports *and* DSA ports
need to share a common address database, in order to switch a frame to
the correct interconnected device.

This is currently working for VLAN filtering aware systems, since Linux
will implement a bridge group as a 802.1Q VLAN, which has its own FDB,
including DSA and CPU links as members.

However when the system doesn't support VLAN filtering, Linux only
relies on the port-based VLAN to implement a bridge group.

To fix hardware cross-chip bridging for such systems, set the same
default address database 0 for user and DSA ports, instead of giving
them all a different default database.

Note that the bridging code prevents frames to egress between unbridged
ports, and flushes FDB entries of a port when changing its STP state.

Also note that the FID 0 is special and means "all" for ATU operations,
but it's OK since it is used as a default forwarding address database.

Fixes: 2db9ce1f ("net: dsa: mv88e6xxx: assign default FDB to ports")
Fixes: 466dfa07 ("net: dsa: mv88e6xxx: assign dynamic FDB to bridges")
Signed-off-by: NVivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx.c

@@ -2181,27 +2181,10 @@ int mv88e6xxx_port_bridge_join(struct dsa_switch *ds, int port,
 			       struct net_device *bridge)
 {
 	struct mv88e6xxx_priv_state *ps = ds_to_priv(ds);
-	u16 fid;
 	int i, err;
 
 	mutex_lock(&ps->smi_mutex);
 
-	/* Get or create the bridge FID and assign it to the port */
-	for (i = 0; i < ps->num_ports; ++i)
-		if (ps->ports[i].bridge_dev == bridge)
-			break;
-
-	if (i < ps->num_ports)
-		err = _mv88e6xxx_port_fid_get(ds, i, &fid);
-	else
-		err = _mv88e6xxx_fid_new(ds, &fid);
-	if (err)
-		goto unlock;
-
-	err = _mv88e6xxx_port_fid_set(ds, port, fid);
-	if (err)
-		goto unlock;
-
 	/* Assign the bridge and remap each port's VLANTable */
 	ps->ports[port].bridge_dev = bridge;
 
@@ -2213,7 +2196,6 @@ int mv88e6xxx_port_bridge_join(struct dsa_switch *ds, int port,
 		}
 	}
 
-unlock:
 	mutex_unlock(&ps->smi_mutex);
 
 	return err;
@@ -2223,16 +2205,10 @@ void mv88e6xxx_port_bridge_leave(struct dsa_switch *ds, int port)
 {
 	struct mv88e6xxx_priv_state *ps = ds_to_priv(ds);
 	struct net_device *bridge = ps->ports[port].bridge_dev;
-	u16 fid;
 	int i;
 
 	mutex_lock(&ps->smi_mutex);
 
-	/* Give the port a fresh Filtering Information Database */
-	if (_mv88e6xxx_fid_new(ds, &fid) ||
-	    _mv88e6xxx_port_fid_set(ds, port, fid))
-		netdev_warn(ds->ports[port], "failed to assign a new FID\n");
-
 	/* Unassign the bridge and remap each port's VLANTable */
 	ps->ports[port].bridge_dev = NULL;
 
@@ -2558,11 +2534,11 @@ static int mv88e6xxx_setup_port(struct dsa_switch *ds, int port)
 	if (ret)
 		goto abort;
 
-	/* Port based VLAN map: give each port its own address
+	/* Port based VLAN map: give each port the same default address
 	 * database, and allow bidirectional communication between the
 	 * CPU and DSA port(s), and the other ports.
 	 */
-	ret = _mv88e6xxx_port_fid_set(ds, port, port + 1);
+	ret = _mv88e6xxx_port_fid_set(ds, port, 0);
 	if (ret)
 		goto abort;