phy: fix 10/100Mbps operation on 1Gbps-capable links

de1d786 [add support for Xilinx 1000BASE-X phy (GTX)] introduced a
check for the extended status register in order to support
1Gbps-capable PHYs that don't have the 1000BASE-T registers. Since
Extended Status only indicates what the PHY (i.e. the local side) is
capable of, this broke communication with non-1Gbps peers.

Only check the extended status if the 1000BASE-T registers are
actually missing so we don't end up setting speed to 1Gbps even though
the previous test (for the combination of local and peer support for
1Gbps) already indicated we can't do 1Gbps with the current peer.

Signed-off-by: Sascha Silbe <t-uboot@infra-silbe.de>
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>

drivers/net/phy/phy.c

@@ -333,7 +333,15 @@ int genphy_parse_link(struct phy_device *phydev)
 		} else if (lpa & LPA_10FULL)
 			phydev->duplex = DUPLEX_FULL;
 
-		if (mii_reg & BMSR_ESTATEN)
+		/*
+		 * Extended status may indicate that the PHY supports
+		 * 1000BASE-T/X even though the 1000BASE-T registers
+		 * are missing. In this case we can't tell whether the
+		 * peer also supports it, so we only check extended
+		 * status if the 1000BASE-T registers are actually
+		 * missing.
+		 */
+		if ((mii_reg & BMSR_ESTATEN) && !(mii_reg & BMSR_ERCAP))
 			estatus = phy_read(phydev, MDIO_DEVAD_NONE,
 					   MII_ESTATUS);