net: macb: poll for fixed link state in SGMII mode

When using a fixed-link configuration with GEM in SGMII mode, such as
for a chip-to-chip interconnect, the link state was always showing as
established regardless of the actual connectivity state. We can monitor
the pcs_link_state bit in the Network Status register to determine
whether the PCS link state is actually up.
Signed-off-by: Robert Hancock <robert.hancock@calian.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/macb_main.c

@@ -847,6 +847,15 @@ static int macb_phylink_connect(struct macb *bp)
 	return 0;
 }
 
+static void macb_get_pcs_fixed_state(struct phylink_config *config,
+				     struct phylink_link_state *state)
+{
+	struct net_device *ndev = to_net_dev(config->dev);
+	struct macb *bp = netdev_priv(ndev);
+
+	state->link = (macb_readl(bp, NSR) & MACB_BIT(NSR_LINK)) != 0;
+}
+
 /* based on au1000_eth. c*/
 static int macb_mii_probe(struct net_device *dev)
 {
@@ -855,6 +864,11 @@ static int macb_mii_probe(struct net_device *dev)
 	bp->phylink_config.dev = &dev->dev;
 	bp->phylink_config.type = PHYLINK_NETDEV;
 
+	if (bp->phy_interface == PHY_INTERFACE_MODE_SGMII) {
+		bp->phylink_config.poll_fixed_state = true;
+		bp->phylink_config.get_fixed_state = macb_get_pcs_fixed_state;
+	}
+
 	bp->phylink = phylink_create(&bp->phylink_config, bp->pdev->dev.fwnode,
 				     bp->phy_interface, &macb_phylink_ops);
 	if (IS_ERR(bp->phylink)) {