dsa: mv88e6xxx: Don't poll forced interfaces for state changes

When polling for link status, don't consider ports which have a forced
link. Such ports don't monitor their phy or may not even have a phy.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx.c

@@ -395,6 +395,7 @@ void mv88e6xxx_poll_link(struct dsa_switch *ds)
 	for (i = 0; i < DSA_MAX_PORTS; i++) {
 		struct net_device *dev;
 		int uninitialized_var(port_status);
+		int pcs_ctrl;
 		int link;
 		int speed;
 		int duplex;
@@ -404,6 +405,10 @@ void mv88e6xxx_poll_link(struct dsa_switch *ds)
 		if (dev == NULL)
 			continue;
 
+		pcs_ctrl = mv88e6xxx_reg_read(ds, REG_PORT(i), PORT_PCS_CTRL);
+		if (pcs_ctrl < 0 || pcs_ctrl & PORT_PCS_CTRL_FORCE_LINK)
+			continue;
+
 		link = 0;
 		if (dev->flags & IFF_UP) {
 			port_status = mv88e6xxx_reg_read(ds, REG_PORT(i),