net: sh_eth: do not advertise Gigabit capabilities when not available

Not all variants of the sh_eth hardware have Gigabit
support. Unfortunately, the current driver doesn't tell the PHY about
the limited MAC capabilities. Due to this, if you have a Gigabit
capable PHY, the PHY will advertise its Gigabit capability and
establish a link at 1Gbit/s, even though the MAC doesn't support it.

In order to avoid this, we use the recently introduced
phy_set_max_speed() to tell the PHY to not advertise speed higher than
100 MBit/s.

Tested on a SH7786 platform, with a Gigabit PHY.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/renesas/sh_eth.c

@@ -1892,6 +1892,16 @@ static int sh_eth_phy_init(struct net_device *ndev)
 		return PTR_ERR(phydev);
 	}
 
+	/* mask with MAC supported features */
+	if (mdp->cd->register_type != SH_ETH_REG_GIGABIT) {
+		int err = phy_set_max_speed(phydev, SPEED_100);
+		if (err) {
+			netdev_err(ndev, "failed to limit PHY to 100 Mbit/s\n");
+			phy_disconnect(phydev);
+			return err;
+		}
+	}
+
 	phy_attached_info(phydev);
 
 	return 0;