net: phy: marvell: Ensure SGMII auto-negotiation is enabled for 88E1111

When 88E1111 is operating in SGMII mode, auto-negotiation should be enabled
on the SGMII side so that the link will come up properly with PCSes which
normally have auto-negotiation enabled. This is normally the case when the
PHY defaults to SGMII mode at power-up, however if we switched it from some
other mode like 1000Base-X, as may happen in some SFP module situations,
it may not be, particularly for modules which have 1000Base-X
auto-negotiation defaulting to disabled.

Call genphy_check_and_restart_aneg on the fiber page to ensure that auto-
negotiation is properly enabled on the SGMII interface.

Signed-off-by: Robert Hancock <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/phy/marvell.c

···
 	if (err < 0)
 		goto error;
 
-	/* Do not touch the fiber page if we're in copper->sgmii mode */
-	if (phydev->interface == PHY_INTERFACE_MODE_SGMII)
-		return 0;
-
 	/* Then the fiber link */
 	err = marvell_set_page(phydev, MII_MARVELL_FIBER_PAGE);
 	if (err < 0)
 		goto error;
 
-	err = marvell_config_aneg_fiber(phydev);
+	if (phydev->interface == PHY_INTERFACE_MODE_SGMII)
+		/* Do not touch the fiber advertisement if we're in copper->sgmii mode.
+		 * Just ensure that SGMII-side autonegotiation is enabled.
+		 * If we switched from some other mode to SGMII it may not be.
+		 */
+		err = genphy_check_and_restart_aneg(phydev, false);
+	else
+		err = marvell_config_aneg_fiber(phydev);
 	if (err < 0)
 		goto error;