gianfar: Don't reset TBI<->SerDes link if it's already up

The link may be up already via the chip's reset strapping, or though action
of U-Boot, or from the last time the interface was brought up.  Resetting
the link causes it to go down for several seconds.  This can significantly
increase the time from power-on to DHCP completion and a device being
accessible to the network.
Signed-off-by: Trent Piepho <tpiepho@freescale.com>
Acked-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/net/gianfar.c

@@ -591,6 +591,14 @@ static void gfar_configure_serdes(struct net_device *dev)
 	if (bus)
 		mutex_lock(&bus->mdio_lock);
 
+	/* If the link is already up, we must already be ok, and don't need to
+	 * configure and reset the TBI<->SerDes link.  Maybe U-Boot configured
+	 * everything for us?  Resetting it takes the link down and requires
+	 * several seconds for it to come back.
+	 */
+	if (gfar_local_mdio_read(regs, tbipa, MII_BMSR) & BMSR_LSTATUS)
+		goto done;
+
 	/* Single clk mode, mii mode off(for serdes communication) */
 	gfar_local_mdio_write(regs, tbipa, MII_TBICON, TBICON_CLK_SELECT);
 
@@ -601,6 +609,7 @@ static void gfar_configure_serdes(struct net_device *dev)
 	gfar_local_mdio_write(regs, tbipa, MII_BMCR, BMCR_ANENABLE |
 			BMCR_ANRESTART | BMCR_FULLDPLX | BMCR_SPEED1000);
 
+	done:
 	if (bus)
 		mutex_unlock(&bus->mdio_lock);
 }