netdev/of/phy: New function: of_mdio_find_bus().

Add of_mdio_find_bus() which allows an mii_bus to be located given its
associated the device tree node.

This is needed by the follow-on patch to add a driver for MDIO bus
multiplexers.

The of_mdiobus_register() function is modified so that the device tree
node is recorded in the mii_bus. Then we can find it again by
iterating over all mdio_bus_class devices.

Because the OF device tree has now become an integral part of the
kernel, this can live in mdio_bus.c (which contains the needed
mdio_bus_class structure) instead of of_mdio.c.

Signed-off-by: David Daney <[e-mail]>
Cc: Grant Likely <[e-mail]>
Cc: "David S. Miller" <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/phy/mdio_bus.c

···
 	.dev_release	= mdiobus_release,
 };
 
+#ifdef CONFIG_OF_MDIO
+/* Helper function for of_mdio_find_bus */
+static int of_mdio_bus_match(struct device *dev, void *mdio_bus_np)
+{
+	return dev->of_node == mdio_bus_np;
+}
+/**
+ * of_mdio_find_bus - Given an mii_bus node, find the mii_bus.
+ * @mdio_np: Pointer to the mii_bus.
+ *
+ * Returns a pointer to the mii_bus, or NULL if none found.
+ *
+ * Because the association of a device_node and mii_bus is made via
+ * of_mdiobus_register(), the mii_bus cannot be found before it is
+ * registered with of_mdiobus_register().
+ *
+ */
+struct mii_bus *of_mdio_find_bus(struct device_node *mdio_bus_np)
+{
+	struct device *d;
+
+	if (!mdio_bus_np)
+		return NULL;
+
+	d = class_find_device(&mdio_bus_class, NULL,  mdio_bus_np,
+			      of_mdio_bus_match);
+
+	return d ? to_mii_bus(d) : NULL;
+}
+EXPORT_SYMBOL(of_mdio_find_bus);
+#endif
+
 /**
  * mdiobus_register - bring up all the PHYs on a given bus and attach them to bus
  * @bus: target mii_bus

drivers/of/of_mdio.c

···
 		for (i=0; i<PHY_MAX_ADDR; i++)
 			mdio->irq[i] = PHY_POLL;
 
+	mdio->dev.of_node = np;
+
 	/* Register the MDIO bus */
 	rc = mdiobus_register(mdio);
 	if (rc)

include/linux/of_mdio.h

···
 					 void (*hndlr)(struct net_device *),
 					 phy_interface_t iface);
 
+extern struct mii_bus *of_mdio_find_bus(struct device_node *mdio_np);
+
 #endif /* __LINUX_OF_MDIO_H */