net: dsa: Do not clobber PHY link outside of state machine

Calling phy_read_status() means that we may call into
genphy_read_status() which in turn will use genphy_update_link() which
can make changes to phydev->link outside of the state machine's state
transitions. This is an invalid behavior that is now caught as of
811a9191 ("phy state machine: failsafe leave invalid RUNNING state")
Reported-by: Zefir Kurtisi <zefir.kurtisi@neratec.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/slave.c

@@ -684,14 +684,10 @@ dsa_slave_get_link_ksettings(struct net_device *dev,
 			     struct ethtool_link_ksettings *cmd)
 {
 	struct dsa_slave_priv *p = netdev_priv(dev);
-	int err;
+	int err = -EOPNOTSUPP;
 
-	err = -EOPNOTSUPP;
-	if (p->phy != NULL) {
-		err = phy_read_status(p->phy);
-		if (err == 0)
+	if (p->phy != NULL)
 		err = phy_ethtool_ksettings_get(p->phy, cmd);
-	}
 
 	return err;
 }