stmmac: create of compatible mdio bus for stmmac driver

The DSA driver needs to be passed a reference to an mdio bus. Typically
the mac is configured to use a fixed link but the mdio bus still needs
to be registered so that it con configure the switch.
This patch follows the same process as the altera tse ethernet driver for
creation of the mdio bus.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Phil Reid <preid@electromag.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/stmmac.txt

@@ -47,6 +47,7 @@ Optional properties:
 - snps,burst_len: The AXI burst lenth value of the AXI BUS MODE register.
 - tx-fifo-depth: See ethernet.txt file in the same directory
 - rx-fifo-depth: See ethernet.txt file in the same directory
+- mdio: with compatible = "snps,dwmac-mdio", create and register mdio bus.
 
 Examples:
 
@@ -65,4 +66,11 @@ Examples:
 		tx-fifo-depth = <16384>;
 		clocks = <&clock>;
 		clock-names = "stmmaceth";
+		mdio0 {
+			#address-cells = <1>;
+			#size-cells = <0>;
+			compatible = "snps,dwmac-mdio";
+			phy1: ethernet-phy@0 {
+			};
+		};
 	};

drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c

@@ -29,7 +29,7 @@
 #include <linux/slab.h>
 #include <linux/of.h>
 #include <linux/of_gpio.h>
-
+#include <linux/of_mdio.h>
 #include <asm/io.h>
 
 #include "stmmac.h"
@@ -200,10 +200,29 @@ int stmmac_mdio_register(struct net_device *ndev)
 	struct stmmac_priv *priv = netdev_priv(ndev);
 	struct stmmac_mdio_bus_data *mdio_bus_data = priv->plat->mdio_bus_data;
 	int addr, found;
+	struct device_node *mdio_node = NULL;
+	struct device_node *child_node = NULL;
 
 	if (!mdio_bus_data)
 		return 0;
 
+	if (IS_ENABLED(CONFIG_OF)) {
+		for_each_child_of_node(priv->device->of_node, child_node) {
+			if (of_device_is_compatible(child_node,
+						    "snps,dwmac-mdio")) {
+				mdio_node = child_node;
+				break;
+			}
+		}
+
+		if (mdio_node) {
+			netdev_dbg(ndev, "FOUND MDIO subnode\n");
+		} else {
+			netdev_err(ndev, "NO MDIO subnode\n");
+			return 0;
+		}
+	}
+
 	new_bus = mdiobus_alloc();
 	if (new_bus == NULL)
 		return -ENOMEM;
@@ -231,7 +250,8 @@ int stmmac_mdio_register(struct net_device *ndev)
 	new_bus->irq = irqlist;
 	new_bus->phy_mask = mdio_bus_data->phy_mask;
 	new_bus->parent = priv->device;
-	err = mdiobus_register(new_bus);
+
+	err = of_mdiobus_register(new_bus, mdio_node);
 	if (err != 0) {
 		pr_err("%s: Cannot register as MDIO bus\n", new_bus->name);
 		goto bus_register_fail;
@@ -284,7 +304,7 @@ int stmmac_mdio_register(struct net_device *ndev)
 		}
 	}
 
-	if (!found) {
+	if (!found && !mdio_node) {
 		pr_warn("%s: No PHY found\n", ndev->name);
 		mdiobus_unregister(new_bus);
 		mdiobus_free(new_bus);

drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c

@@ -146,7 +146,7 @@ stmmac_probe_config_dt(struct platform_device *pdev, const char **mac)
 	if (of_property_read_u32(np, "snps,phy-addr", &plat->phy_addr) == 0)
 		dev_warn(&pdev->dev, "snps,phy-addr property is deprecated\n");
 
-	if (plat->phy_node || plat->phy_bus_name)
+	if ((plat->phy_node && !of_phy_is_fixed_link(np)) || plat->phy_bus_name)
 		plat->mdio_bus_data = NULL;
 	else
 		plat->mdio_bus_data =