net: dsa: OF-ware slave_mii_bus

If found, register the DSA internally allocated slave_mii_bus with an OF
"mdio" child object. It can save some drivers from creating their
custom internal MDIO bus.
Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/dsa2.c

@@ -13,6 +13,7 @@
 #include <linux/slab.h>
 #include <linux/rtnetlink.h>
 #include <linux/of.h>
+#include <linux/of_mdio.h>
 #include <linux/of_net.h>
 #include <net/devlink.h>
 #include <net/sch_generic.h>
@@ -852,6 +853,7 @@ static int dsa_switch_setup_tag_protocol(struct dsa_switch *ds)
 static int dsa_switch_setup(struct dsa_switch *ds)
 {
 	struct dsa_devlink_priv *dl_priv;
+	struct device_node *dn;
 	struct dsa_port *dp;
 	int err;
 
@@ -907,7 +909,10 @@ static int dsa_switch_setup(struct dsa_switch *ds)
 
 		dsa_slave_mii_bus_init(ds);
 
-		err = mdiobus_register(ds->slave_mii_bus);
+		dn = of_get_child_by_name(ds->dev->of_node, "mdio");
+
+		err = of_mdiobus_register(ds->slave_mii_bus, dn);
+		of_node_put(dn);
 		if (err < 0)
 			goto free_slave_mii_bus;
 	}