net: phylink: disable BMCR_ISOLATE in phylink_mii_c22_pcs_config

The Xilinx PCS/PMA PHY requires that BMCR_ISOLATE be disabled for proper
operation in 1000BaseX mode. It should be safe to ensure this bit is
disabled in phylink_mii_c22_pcs_config in all cases.
Signed-off-by: Robert Hancock <robert.hancock@calian.com>
Reviewed-by: Russell King <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20201026175802.1332477-1-robert.hancock@calian.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/phylink.c

@@ -2515,9 +2515,10 @@ int phylink_mii_c22_pcs_config(struct mdio_device *pcs, unsigned int mode,
 
 	changed = ret > 0;
 
+	/* Ensure ISOLATE bit is disabled */
 	bmcr = mode == MLO_AN_INBAND ? BMCR_ANENABLE : 0;
 	ret = mdiobus_modify(pcs->bus, pcs->addr, MII_BMCR,
-			     BMCR_ANENABLE, bmcr);
+			     BMCR_ANENABLE | BMCR_ISOLATE, bmcr);
 	if (ret < 0)
 		return ret;