dp83640: Ensure against premature access to PHY registers after reset

The datasheet specifies a 3uS pause after performing a software
reset. The default implementation of genphy_soft_reset() does not
provide this, so implement soft_reset with the needed pause.
Signed-off-by: Esben Haabendal <eha@deif.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/dp83640.c

@@ -1207,6 +1207,23 @@ static void dp83640_remove(struct phy_device *phydev)
 	kfree(dp83640);
 }
 
+static int dp83640_soft_reset(struct phy_device *phydev)
+{
+	int ret;
+
+	ret = genphy_soft_reset(phydev);
+	if (ret < 0)
+		return ret;
+
+	/* From DP83640 datasheet: "Software driver code must wait 3 us
+	 * following a software reset before allowing further serial MII
+	 * operations with the DP83640."
+	 */
+	udelay(10);		/* Taking udelay inaccuracy into account */
+
+	return 0;
+}
+
 static int dp83640_config_init(struct phy_device *phydev)
 {
 	struct dp83640_private *dp83640 = phydev->priv;
@@ -1501,6 +1518,7 @@ static struct phy_driver dp83640_driver = {
 	.flags		= PHY_HAS_INTERRUPT,
 	.probe		= dp83640_probe,
 	.remove		= dp83640_remove,
+	.soft_reset	= dp83640_soft_reset,
 	.config_init	= dp83640_config_init,
 	.ack_interrupt  = dp83640_ack_interrupt,
 	.config_intr    = dp83640_config_intr,