net: dsa: mv88e6xxx: don't use devres for mdiobus

As explained in commits:
74b6d7d ("net: dsa: realtek: register the MDIO bus under devres")
5135e96 ("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 mv88e6xxx is an MDIO 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 Marvell switch driver on shutdown.

systemd-shutdown[1]: Powering off.
mv88e6085 0x0000000008b96000:00 sw_gl0: Link is Down
fsl-mc dpbp.9: Removing from iommu group 7
fsl-mc dpbp.8: Removing from iommu group 7
------------[ cut here ]------------
kernel BUG at drivers/net/phy/mdio_bus.c:677!
Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 1 Comm: systemd-shutdow Not tainted 5.16.5-00040-gdc05f73788e5 xen-troops#15
pc : mdiobus_free+0x44/0x50
lr : devm_mdiobus_free+0x10/0x20
Call trace:
 mdiobus_free+0x44/0x50
 devm_mdiobus_free+0x10/0x20
 devres_release_all+0xa0/0x100
 __device_release_driver+0x190/0x220
 device_release_driver_internal+0xac/0xb0
 device_links_unbind_consumers+0xd4/0x100
 __device_release_driver+0x4c/0x220
 device_release_driver_internal+0xac/0xb0
 device_links_unbind_consumers+0xd4/0x100
 __device_release_driver+0x94/0x220
 device_release_driver+0x28/0x40
 bus_remove_device+0x118/0x124
 device_del+0x174/0x420
 fsl_mc_device_remove+0x24/0x40
 __fsl_mc_device_remove+0xc/0x20
 device_for_each_child+0x58/0xa0
 dprc_remove+0x90/0xb0
 fsl_mc_driver_remove+0x20/0x5c
 __device_release_driver+0x21c/0x220
 device_release_driver+0x28/0x40
 bus_remove_device+0x118/0x124
 device_del+0x174/0x420
 fsl_mc_bus_remove+0x80/0x100
 fsl_mc_bus_shutdown+0xc/0x1c
 platform_shutdown+0x20/0x30
 device_shutdown+0x154/0x330
 kernel_power_off+0x34/0x6c
 __do_sys_reboot+0x15c/0x250
 __arm64_sys_reboot+0x20/0x30
 invoke_syscall.constprop.0+0x4c/0xe0
 do_el0_svc+0x4c/0x150
 el0_svc+0x24/0xb0
 el0t_64_sync_handler+0xa8/0xb0
 el0t_64_sync+0x178/0x17c

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 Marvell driver already has a good structure for mdiobus removal, so
just plug in mdiobus_free and get rid of devres.

Fixes: ac3a68d ("net: phy: don't abuse devres in devm_mdiobus_register()")
Reported-by: Rafael Richter <[email protected]>
Signed-off-by: Vladimir Oltean <[email protected]>
Tested-by: Daniel Klauer <[email protected]>
Reviewed-by: Andrew Lunn <[email protected]>
Reviewed-by: Florian Fainelli <[email protected]>
Signed-off-by: Jakub Kicinski <[email protected]>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -3399,7 +3399,7 @@ static int mv88e6xxx_mdio_register(struct mv88e6xxx_chip *chip,
 			return err;
 	}
 
-	bus = devm_mdiobus_alloc_size(chip->dev, sizeof(*mdio_bus));
+	bus = mdiobus_alloc_size(sizeof(*mdio_bus));
 	if (!bus)
 		return -ENOMEM;
 
@@ -3424,14 +3424,14 @@ static int mv88e6xxx_mdio_register(struct mv88e6xxx_chip *chip,
 	if (!external) {
 		err = mv88e6xxx_g2_irq_mdio_setup(chip, bus);
 		if (err)
-			return err;
+			goto out;
 	}
 
 	err = of_mdiobus_register(bus, np);
 	if (err) {
 		dev_err(chip->dev, "Cannot register MDIO bus (%d)\n", err);
 		mv88e6xxx_g2_irq_mdio_free(chip, bus);
-		return err;
+		goto out;
 	}
 
 	if (external)
@@ -3440,6 +3440,10 @@ static int mv88e6xxx_mdio_register(struct mv88e6xxx_chip *chip,
 		list_add(&mdio_bus->list, &chip->mdios);
 
 	return 0;
+
+out:
+	mdiobus_free(bus);
+	return err;
 }
 
 static void mv88e6xxx_mdios_unregister(struct mv88e6xxx_chip *chip)
@@ -3455,6 +3459,7 @@ static void mv88e6xxx_mdios_unregister(struct mv88e6xxx_chip *chip)
 			mv88e6xxx_g2_irq_mdio_free(chip, bus);
 
 		mdiobus_unregister(bus);
+		mdiobus_free(bus);
 	}
 }