net: asix: fix modprobe "sysfs: cannot create duplicate filename"

"modprobe asix ; rmmod asix ; modprobe asix" fails with:
sysfs: cannot create duplicate filename \
'/devices/virtual/mdio_bus/usb-003:004'

Issue was originally reported by Anton Lundin on 2022-06-22 (link below).

Chrome OS team hit the same issue in Feb, 2023 when trying to find
work arounds for other issues with AX88172 devices.

The use of devm_mdiobus_register() with usbnet devices results in the
MDIO data being associated with the USB device. When the asix driver
is unloaded, the USB device continues to exist and the corresponding
"mdiobus_unregister()" is NOT called until the USB device is unplugged
or unauthorized. So the next "modprobe asix" will fail because the MDIO
phy sysfs attributes still exist.

The 'easy' (from a design PoV) fix is to use the non-devm variants of
mdiobus_* functions and explicitly manage this use in the asix_bind
and asix_unbind function calls. I've not explored trying to fix usbnet
initialization so devm_* stuff will work.

Fixes: e532a096be0e5 ("net: usb: asix: ax88772: add phylib support")
Reported-by: Anton Lundin <[e-mail]>
Link: https://lore.kernel.org/netdev/[e-mail]/T/
Tested-by: Eizan Miyamoto <[e-mail]>
Signed-off-by: Grant Grundler <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/usb/asix_devices.c

···
 static int ax88772_init_mdio(struct usbnet *dev)
 {
 	struct asix_common_private *priv = dev->driver_priv;
+	int ret;
 
-	priv->mdio = devm_mdiobus_alloc(&dev->udev->dev);
+	priv->mdio = mdiobus_alloc();
 	if (!priv->mdio)
 		return -ENOMEM;
 
···
 	snprintf(priv->mdio->id, MII_BUS_ID_SIZE, "usb-%03d:%03d",
 		 dev->udev->bus->busnum, dev->udev->devnum);
 
-	return devm_mdiobus_register(&dev->udev->dev, priv->mdio);
+	ret = mdiobus_register(priv->mdio);
+	if (ret) {
+		netdev_err(dev->net, "Could not register MDIO bus (err %d)\n", ret);
+		mdiobus_free(priv->mdio);
+		priv->mdio = NULL;
+	}
+
+	return ret;
+}
+
+static void ax88772_mdio_unregister(struct asix_common_private *priv)
+{
+	mdiobus_unregister(priv->mdio);
+	mdiobus_free(priv->mdio);
 }
 
 static int ax88772_init_phy(struct usbnet *dev)
···
 
 	ret = ax88772_init_mdio(dev);
 	if (ret)
-		return ret;
+		goto mdio_err;
 
 	ret = ax88772_phylink_setup(dev);
 	if (ret)
-		return ret;
+		goto phylink_err;
 
 	ret = ax88772_init_phy(dev);
 	if (ret)
-		phylink_destroy(priv->phylink);
+		goto initphy_err;
 
+	return 0;
+
+initphy_err:
+	phylink_destroy(priv->phylink);
+phylink_err:
+	ax88772_mdio_unregister(priv);
+mdio_err:
 	return ret;
 }
 
···
 	phylink_disconnect_phy(priv->phylink);
 	rtnl_unlock();
 	phylink_destroy(priv->phylink);
+	ax88772_mdio_unregister(priv);
 	asix_rx_fixup_common_free(dev->driver_priv);
 }