of: mdio: Support fixed links in of_phy_get_and_connect()

By a simple extension of of_phy_get_and_connect() drivers
that have a fixed link on e.g. RGMII can support also
fixed links, so in addition to:

ethernet-port {
	phy-mode = "rgmii";
	phy-handle = <&foo>;
};

This setup with a fixed-link node and no phy-handle will
now also work just fine:

ethernet-port {
	phy-mode = "rgmii";
	fixed-link {
		speed = <1000>;
		full-duplex;
		pause;
	};
};

This is very helpful for connecting random ethernet ports
to e.g. DSA switches that typically reside on fixed links.

The phy-mode is still there as the fixes link in this case
is still an RGMII link.

Tested on the Cortina Gemini driver with the Vitesse DSA
router chip on a fixed 1Gbit link.
Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/of/of_mdio.c

@@ -367,14 +367,23 @@ struct phy_device *of_phy_get_and_connect(struct net_device *dev,
 	phy_interface_t iface;
 	struct device_node *phy_np;
 	struct phy_device *phy;
+	int ret;
 
 	iface = of_get_phy_mode(np);
 	if (iface < 0)
 		return NULL;
-
+	if (of_phy_is_fixed_link(np)) {
+		ret = of_phy_register_fixed_link(np);
+		if (ret < 0) {
+			netdev_err(dev, "broken fixed-link specification\n");
+			return NULL;
+		}
+		phy_np = of_node_get(np);
+	} else {
 		phy_np = of_parse_phandle(np, "phy-handle", 0);
 		if (!phy_np)
 			return NULL;
+	}
 
 	phy = of_phy_connect(dev, phy_np, hndlr, 0, iface);