net: usb: asix: allow optionally getting mac address from device tree

For Embedded use where e.g. AX88772B chips may be used without external
EEPROMs the boot loader may choose to pass the MAC address to be used
via device tree. Therefore, allow for optionally getting the MAC
address from device tree data e.g. as follows (excerpt from a T30 based
board, local-mac-address to be filled in by boot loader):

/* EHCI instance 1: USB2_DP/N -> AX88772B */
usb@7d004000 {
	status = "okay";
	#address-cells = <1>;
	#size-cells = <0>;
	asix@1 {
		reg = <1>;
		local-mac-address = [00 00 00 00 00 00];
	};
};
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/asix_devices.c

@@ -691,24 +691,32 @@ static int ax88772_bind(struct usbnet *dev, struct usb_interface *intf)
 	u32 phyid;
 	struct asix_common_private *priv;
 
-	usbnet_get_endpoints(dev,intf);
+	usbnet_get_endpoints(dev, intf);
 
-	/* Get the MAC address */
-	if (dev->driver_info->data & FLAG_EEPROM_MAC) {
-		for (i = 0; i < (ETH_ALEN >> 1); i++) {
-			ret = asix_read_cmd(dev, AX_CMD_READ_EEPROM, 0x04 + i,
-					    0, 2, buf + i * 2, 0);
-			if (ret < 0)
-				break;
-		}
+	/* Maybe the boot loader passed the MAC address via device tree */
+	if (!eth_platform_get_mac_address(&dev->udev->dev, buf)) {
+		netif_dbg(dev, ifup, dev->net,
+			  "MAC address read from device tree");
 	} else {
-		ret = asix_read_cmd(dev, AX_CMD_READ_NODE_ID,
-				0, 0, ETH_ALEN, buf, 0);
-	}
+		/* Try getting the MAC address from EEPROM */
+		if (dev->driver_info->data & FLAG_EEPROM_MAC) {
+			for (i = 0; i < (ETH_ALEN >> 1); i++) {
+				ret = asix_read_cmd(dev, AX_CMD_READ_EEPROM,
+						    0x04 + i, 0, 2, buf + i * 2,
+						    0);
+				if (ret < 0)
+					break;
+			}
+		} else {
+			ret = asix_read_cmd(dev, AX_CMD_READ_NODE_ID,
+					    0, 0, ETH_ALEN, buf, 0);
+		}
 
-	if (ret < 0) {
-		netdev_dbg(dev->net, "Failed to read MAC address: %d\n", ret);
-		return ret;
+		if (ret < 0) {
+			netdev_dbg(dev->net, "Failed to read MAC address: %d\n",
+				   ret);
+			return ret;
+		}
 	}
 
 	asix_set_netdev_dev_addr(dev, buf);