dm9601: handle corrupt mac address

Some cheap devices ship with dangling EEPROM pins!
They always return invalid address ff:ff:ff:ff:ff:ff.

Inherit the auto-generated address in this case,
so that these products can work with zero configuration.
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/dm9601.c

@@ -414,6 +414,7 @@ static int dm9601_set_mac_address(struct net_device *net, void *p)
 static int dm9601_bind(struct usbnet *dev, struct usb_interface *intf)
 {
 	int ret;
+	u8 mac[ETH_ALEN];
 
 	ret = usbnet_get_endpoints(dev, intf);
 	if (ret)
@@ -438,12 +439,18 @@ static int dm9601_bind(struct usbnet *dev, struct usb_interface *intf)
 	udelay(20);
 
 	/* read MAC */
-	if (dm_read(dev, DM_PHY_ADDR, ETH_ALEN, dev->net->dev_addr) < 0) {
+	if (dm_read(dev, DM_PHY_ADDR, ETH_ALEN, mac) < 0) {
 		printk(KERN_ERR "Error reading MAC address\n");
 		ret = -ENODEV;
 		goto out;
 	}
 
+	/*
+	 * Overwrite the auto-generated address only with good ones.
+	 */
+	if (is_valid_ether_addr(mac))
+		memcpy(dev->net->dev_addr, mac, ETH_ALEN);
+
 	/* power up phy */
 	dm_write_reg(dev, DM_GPR_CTRL, 1);
 	dm_write_reg(dev, DM_GPR_DATA, 0);