net: nixge: Make mdio child node optional

Make MDIO child optional and only instantiate the
MDIO bus if the child is actually present.

There are currently no (in-tree) users of this
binding; all (out-of-tree) users use overlays that
get shipped together with the FPGA images that contain
the IP.

This will significantly increase maintainabilty
of future revisions of this IP.

Reviewed-by: Andrew Lunn <[e-mail]>
Signed-off-by: Moritz Fischer <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/devicetree/bindings/net/nixge.txt

···
 - nvmem-cells: Phandle of nvmem cell containing the MAC address
 - nvmem-cell-names: Should be "address"
 
+Optional properties:
+- mdio subnode to indicate presence of MDIO controller
+
 Examples (10G generic PHY):
 	nixge0: ethernet@40000000 {
 		compatible = "ni,xge-enet-3.00";
···
 		phy-mode = "xgmii";
 		phy-handle = <&ethernet_phy1>;
 
-		ethernet_phy1: ethernet-phy@4 {
-			compatible = "ethernet-phy-ieee802.3-c45";
-			reg = <4>;
+		mdio {
+			ethernet_phy1: ethernet-phy@4 {
+				compatible = "ethernet-phy-ieee802.3-c45";
+				reg = <4>;
+			};
 		};
+	};
+
+Examples (10G generic PHY, no MDIO):
+	nixge0: ethernet@40000000 {
+		compatible = "ni,xge-enet-2.00";
+		reg = <0x40000000 0x6000>;
+
+		nvmem-cells = <&eth1_addr>;
+		nvmem-cell-names = "address";
+
+		interrupts = <0 29 IRQ_TYPE_LEVEL_HIGH>, <0 30 IRQ_TYPE_LEVEL_HIGH>;
+		interrupt-names = "rx", "tx";
+		interrupt-parent = <&intc>;
+
+		phy-mode = "xgmii";
+		phy-handle = <&ethernet_phy1>;
 	};

drivers/net/ethernet/ni/nixge.c

···
 {
 	struct nixge_priv *priv;
 	struct net_device *ndev;
+	struct device_node *mn;
 	const u8 *mac_addr;
 	int err;
 
···
 	priv->coalesce_count_rx = XAXIDMA_DFT_RX_THRESHOLD;
 	priv->coalesce_count_tx = XAXIDMA_DFT_TX_THRESHOLD;
 
-	err = nixge_mdio_setup(priv, pdev->dev.of_node);
-	if (err) {
-		netdev_err(ndev, "error registering mdio bus");
-		goto free_netdev;
+	mn = of_get_child_by_name(pdev->dev.of_node, "mdio");
+	if (mn) {
+		err = nixge_mdio_setup(priv, mn);
+		of_node_put(mn);
+		if (err) {
+			netdev_err(ndev, "error registering mdio bus");
+			goto free_netdev;
+		}
 	}
 
 	priv->phy_mode = of_get_phy_mode(pdev->dev.of_node);
···
 	return 0;
 
 unregister_mdio:
-	mdiobus_unregister(priv->mii_bus);
+	if (priv->mii_bus)
+		mdiobus_unregister(priv->mii_bus);
 
 free_netdev:
 	free_netdev(ndev);
···
 
 	unregister_netdev(ndev);
 
-	mdiobus_unregister(priv->mii_bus);
+	if (priv->mii_bus)
+		mdiobus_unregister(priv->mii_bus);
 
 	free_netdev(ndev);