of: of_mdio: Ensure mdio device is a PHY

of_phy_find_device() is used to find the phy device associated with a
device node. It is expected the node is for a PHY device, but in fact
it could of been probed as a generic MDIO device. Ensure the device is
a PHY before returning it.

Fixes: a9049e0c51 ("mdio: Add support for mdio drivers.")
Reported-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Reported-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/of/of_mdio.c

@@ -256,11 +256,19 @@ static int of_phy_match(struct device *dev, void *phy_np)
 struct phy_device *of_phy_find_device(struct device_node *phy_np)
 {
 	struct device *d;
+	struct mdio_device *mdiodev;
+
 	if (!phy_np)
 		return NULL;
 
 	d = bus_find_device(&mdio_bus_type, NULL, phy_np, of_phy_match);
-	return d ? to_phy_device(d) : NULL;
+	if (d) {
+		mdiodev = to_mdio_device(d);
+		if (mdiodev->flags & MDIO_DEVICE_FLAG_PHY)
+			return to_phy_device(d);
+	}
+
+	return NULL;
 }
 EXPORT_SYMBOL(of_phy_find_device);