net: phy: add device-managed devm_mdiobus_register

If there's no special ordering requirement for mdiobus_unregister(),
then driver code can be simplified by using a device-managed version
of mdiobus_register(). Prerequisite is that bus allocation has been
done device-managed too. Else mdiobus_free() may be called whilst
bus is still registered, resulting in a BUG_ON(). Therefore let
devm_mdiobus_register() return -EPERM if bus was allocated
non-managed.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/mdio_bus.c

@@ -170,7 +170,12 @@ EXPORT_SYMBOL(mdiobus_alloc_size);
 
 static void _devm_mdiobus_free(struct device *dev, void *res)
 {
-	mdiobus_free(*(struct mii_bus **)res);
+	struct mii_bus *bus = *(struct mii_bus **)res;
+
+	if (bus->is_managed_registered && bus->state == MDIOBUS_REGISTERED)
+		mdiobus_unregister(bus);
+
+	mdiobus_free(bus);
 }
 
 static int devm_mdiobus_match(struct device *dev, void *res, void *data)
@@ -210,6 +215,7 @@ struct mii_bus *devm_mdiobus_alloc_size(struct device *dev, int sizeof_priv)
 	if (bus) {
 		*ptr = bus;
 		devres_add(dev, ptr);
+		bus->is_managed = 1;
 	} else {
 		devres_free(ptr);
 	}

include/linux/phy.h

@@ -241,6 +241,9 @@ struct mii_bus {
 	int (*reset)(struct mii_bus *bus);
 	struct mdio_bus_stats stats[PHY_MAX_ADDR];
 
+	unsigned int is_managed:1;	/* is device-managed */
+	unsigned int is_managed_registered:1;
+
 	/*
 	 * A lock to ensure that only one thing can read/write
 	 * the MDIO bus at a time
@@ -286,6 +289,20 @@ static inline struct mii_bus *mdiobus_alloc(void)
 
 int __mdiobus_register(struct mii_bus *bus, struct module *owner);
 #define mdiobus_register(bus) __mdiobus_register(bus, THIS_MODULE)
+static inline int devm_mdiobus_register(struct mii_bus *bus)
+{
+	int ret;
+
+	if (!bus->is_managed)
+		return -EPERM;
+
+	ret = mdiobus_register(bus);
+	if (!ret)
+		bus->is_managed_registered = 1;
+
+	return ret;
+}
+
 void mdiobus_unregister(struct mii_bus *bus);
 void mdiobus_free(struct mii_bus *bus);
 struct mii_bus *devm_mdiobus_alloc_size(struct device *dev, int sizeof_priv);