net: dsa: seville: register the mdiobus under devres

As explained in commits:
74b6d7d1 ("net: dsa: realtek: register the MDIO bus under devres")
5135e96a ("net: dsa: don't allocate the slave_mii_bus using devres")

mdiobus_free() will panic when called from devm_mdiobus_free() <-
devres_release_all() <- __device_release_driver(), and that mdiobus was
not previously unregistered.

The Seville VSC9959 switch is a platform device, so the initial set of
constraints that I thought would cause this (I2C or SPI buses which call
->remove on ->shutdown) do not apply. But there is one more which
applies here.

If the DSA master itself is on a bus that calls ->remove from ->shutdown
(like dpaa2-eth, which is on the fsl-mc bus), there is a device link
between the switch and the DSA master, and device_links_unbind_consumers()
will unbind the seville switch driver on shutdown.

So the same treatment must be applied to all DSA switch drivers, which
is: either use devres for both the mdiobus allocation and registration,
or don't use devres at all.

The seville driver has a code structure that could accommodate both the
mdiobus_unregister and mdiobus_free calls, but it has an external
dependency upon mscc_miim_setup() from mdio-mscc-miim.c, which calls
devm_mdiobus_alloc_size() on its behalf. So rather than restructuring
that, and exporting yet one more symbol mscc_miim_teardown(), let's work
with devres and replace of_mdiobus_register with the devres variant.
When we use all-devres, we can ensure that devres doesn't free a
still-registered bus (it either runs both callbacks, or none).

Fixes: ac3a68d5 ("net: phy: don't abuse devres in devm_mdiobus_register()")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/ocelot/seville_vsc9953.c

@@ -1029,7 +1029,7 @@ static int vsc9953_mdio_bus_alloc(struct ocelot *ocelot)
 	}
 
 	/* Needed in order to initialize the bus mutex lock */
-	rc = of_mdiobus_register(bus, NULL);
+	rc = devm_of_mdiobus_register(dev, bus, NULL);
 	if (rc < 0) {
 		dev_err(dev, "failed to register MDIO bus\n");
 		return rc;
@@ -1083,7 +1083,8 @@ static void vsc9953_mdio_bus_free(struct ocelot *ocelot)
 		mdio_device_free(mdio_device);
 		lynx_pcs_destroy(phylink_pcs);
 	}
-	mdiobus_unregister(felix->imdio);
+
+	/* mdiobus_unregister and mdiobus_free handled by devres */
 }
 
 static const struct felix_info seville_info_vsc9953 = {