[PATCHv2 1/2] TEST:net: asix: fix modprobe "sysfs: cannot create duplicate filename"

[Grant Grundler]

"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 14:16 UTC:
   https://lore.kernel.org/netdev/20220623063649.GD23685@xxxxxxxxxxxxxx/T/

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 <glance@xxxxxxxxxx>
Tested-by: Eizan Miyamoto <eizan@xxxxxxxxxxxx>
Signed-off-by: Grant Grundler <grundler@xxxxxxxxxxxx>
---
 drivers/net/usb/asix_devices.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

V2: moved mdiobus_get_phy() call back into ax88772_init_phy()
   Lukas Wunner is entirely correct this patch is much easier
   to backport without this patch hunk.
   Added "Fixes:" tag per request from Florian Fainelli

diff --git a/drivers/net/usb/asix_devices.c b/drivers/net/usb/asix_devices.c
index 30e87389aefa1..21845b88a64b9 100644
--- a/drivers/net/usb/asix_devices.c
+++ b/drivers/net/usb/asix_devices.c
@@ -640,8 +640,9 @@ static int asix_resume(struct usb_interface *intf)
 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;
 
@@ -653,7 +654,20 @@ static int ax88772_init_mdio(struct usbnet *dev)
 	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)
@@ -664,6 +678,7 @@ static int ax88772_init_phy(struct usbnet *dev)
 	priv->phydev = mdiobus_get_phy(priv->mdio, priv->phy_addr);
 	if (!priv->phydev) {
 		netdev_err(dev->net, "Could not find PHY\n");
+		ax88772_mdio_unregister(priv);
 		return -ENODEV;
 	}
 
@@ -805,6 +820,7 @@ static void ax88772_unbind(struct usbnet *dev, struct usb_interface *intf)
 	struct asix_common_private *priv = dev->driver_priv;
 
 	phy_disconnect(priv->phydev);
+	ax88772_mdio_unregister(priv);
 	asix_rx_fixup_common_free(dev->driver_priv);
 }
 
-- 
2.39.2