net: arc: rockchip: fix emac mdio node support

The binding emac_rockchip.txt is converted to YAML.
Changed against the original binding is an added MDIO subnode.
This make the driver failed to find the PHY, and given the 'mdio
has invalid PHY address' it is probably looking in the wrong node.
Fix emac_mdio.c so that it can handle both old and new
device trees.

Fixes: 1dabb74 ("ARM: dts: rockchip: restyle emac nodes")
Signed-off-by: Johan Jonker <[email protected]>
Tested-by: Andy Yan <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Andy Yan <[email protected]>
Reviewed-by: Andrew Lunn <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>

Author: Johan Jonker

drivers/net/ethernet/arc/emac_mdio.c

@@ -133,6 +133,7 @@ int arc_mdio_probe(struct arc_emac_priv *priv)
 	struct arc_emac_mdio_bus_data *data = &priv->bus_data;
 	struct device_node *np = priv->dev->of_node;
 	const char *name = "Synopsys MII Bus";
+	struct device_node *mdio_node;
 	struct mii_bus *bus;
 	int error;
 
@@ -164,7 +165,13 @@ int arc_mdio_probe(struct arc_emac_priv *priv)
 
 	snprintf(bus->id, MII_BUS_ID_SIZE, "%s", bus->name);
 
-	error = of_mdiobus_register(bus, priv->dev->of_node);
+	/* Backwards compatibility for EMAC nodes without MDIO subnode. */
+	mdio_node = of_get_child_by_name(np, "mdio");
+	if (!mdio_node)
+		mdio_node = of_node_get(np);
+
+	error = of_mdiobus_register(bus, mdio_node);
+	of_node_put(mdio_node);
 	if (error) {
 		mdiobus_free(bus);
 		return dev_err_probe(priv->dev, error,