net: dsa: mv88e6xxx: Disable Message Port bit for CPU port

Datasheet says that the Message Port bit should not be set for the CPU port.
Having it set causes DSA tagged packets to be sent to the CPU port roughly
every 30 seconds. Those packets are the same as real packets forwarded between
switch ports if the switch is configured for switching between multiple ports.
The packets are then bridged by the software bridge, resulting in duplicated
packets on the network.
Reported-by: NAndrew Lunn <andrew@lunn.ch>
Cc: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Tested-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx.c

@@ -707,11 +707,10 @@ int mv88e6xxx_setup_port_common(struct dsa_switch *ds, int port)
 
 	mutex_lock(&ps->smi_mutex);
 
-	/* Port Control 1: disable trunking.  Also, if this is the
-	 * CPU port, enable learn messages to be sent to this port.
+	/* Port Control 1: disable trunking, disable sending
+	 * learning messages to this port.
 	 */
-	ret = _mv88e6xxx_reg_write(ds, REG_PORT(port), 0x05,
-				   dsa_is_cpu_port(ds, port) ? 0x8000 : 0x0000);
+	ret = _mv88e6xxx_reg_write(ds, REG_PORT(port), 0x05, 0x0000);
 	if (ret)
 		goto abort;