net: phy: marvell10g: fix 88x3310 power up

Clear MV_V2_PORT_CTRL_PWRDOWN bit to set power up for 88x3310 PHY,
it sometimes does not take effect immediately. And a read of this
register causes the bit not to clear. This will cause mv3310_reset()
to time out, which will fail the config initialization. So add a delay
before the next access.

Fixes: c9cc1c81 ("net: phy: marvell10g: place in powersave mode at probe")
Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/marvell10g.c

@@ -328,6 +328,13 @@ static int mv3310_power_up(struct phy_device *phydev)
 	ret = phy_clear_bits_mmd(phydev, MDIO_MMD_VEND2, MV_V2_PORT_CTRL,
 				 MV_V2_PORT_CTRL_PWRDOWN);
 
+	/* Sometimes, the power down bit doesn't clear immediately, and
+	 * a read of this register causes the bit not to clear. Delay
+	 * 100us to allow the PHY to come out of power down mode before
+	 * the next access.
+	 */
+	udelay(100);
+
 	if (phydev->drv->phy_id != MARVELL_PHY_ID_88X3310 ||
 	    priv->firmware_ver < 0x00030000)
 		return ret;