> diff --git a/Documentation/devicetree/bindings/net/mdio-mux.txt b/Documentation/devicetree/bindings/net/mdio-mux.txt
> new file mode 100644
> index 0000000..a908312
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/net/mdio-mux.txt
> @@ -0,0 +1,132 @@
> +Common MDIO bus multiplexer/switch properties.
> +
> +An MDIO bus multiplexer/switch will have several child busses that are
> +numbered uniquely in a device dependent manner. The nodes for an MDIO
> +bus multiplexer/switch will have one child node for each child bus.
> +
> +Required properties:
> +- parent-bus : phandle to the parent MDIO bus.
Should probably be mdio-parent-bus
> +
> +Optional properties:
> +- Other properties specific to the multiplexer/switch hardware.
> +
> +Required properties for child nodes:
> +- #address-cells = <1>;
> +- #size-cells = <0>;
> +- cell-index : The sub-bus number.
What does sub-bus number mean?
> +
> +
> +Example :
[snip]
> diff --git a/drivers/net/phy/mdio-mux.c b/drivers/net/phy/mdio-mux.c
> new file mode 100644
> index 0000000..f9c5826
> --- /dev/null
> +++ b/drivers/net/phy/mdio-mux.c
> @@ -0,0 +1,182 @@
> +/*
> + * This file is subject to the terms and conditions of the GNU General Public
> + * License. See the file "COPYING" in the main directory of this archive
> + * for more details.
> + *
> + * Copyright (C) 2011 Cavium Networks
> + */
> +
> +#include <linux/platform_device.h>
> +#include <linux/of_mdio.h>
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/gfp.h>
> +#include <linux/phy.h>
> +#include <linux/mdio-mux.h>
> +
> +#define DRV_VERSION "1.0"
> +#define DRV_DESCRIPTION "MDIO bus multiplexer driver"
> +
> +struct mdio_mux_parent_bus {
> + struct mii_bus *mii_bus;
> + int current_child;
> + int parent_id;
> + void *switch_data;
> + int (*switch_fn)(int current_child, int desired_child, void *data);
> +};
> +
> +struct mdio_mux_child_bus {
> + struct mii_bus *mii_bus;
> + struct mdio_mux_parent_bus *parent;
> + int bus_number;
> + int phy_irq[PHY_MAX_ADDR];
> +};
> +
> +/*
> + * The parent bus' lock is used to order access to the switch_fn.
> + */
> +static int mdio_mux_read(struct mii_bus *bus, int phy_id, int regnum)
> +{
> + struct mdio_mux_child_bus *cb = bus->priv;
> + struct mdio_mux_parent_bus *pb = cb->parent;
> + int r;
> +
> + mutex_lock(&pb->mii_bus->mdio_lock);
> + r = pb->switch_fn(pb->current_child, cb->bus_number, pb->switch_data);
> + if (r)
> + goto out;
> +
> + pb->current_child = cb->bus_number;
> +
> + r = pb->mii_bus->read(pb->mii_bus, phy_id, regnum);
> +out:
> + mutex_unlock(&pb->mii_bus->mdio_lock);
> +
> + return r;
> +}
> +
> +/*
> + * The parent bus' lock is used to order access to the switch_fn.
> + */
> +static int mdio_mux_write(struct mii_bus *bus, int phy_id,
> + int regnum, u16 val)
> +{
> + struct mdio_mux_child_bus *cb = bus->priv;
> + struct mdio_mux_parent_bus *pb = cb->parent;
> +
> + int r;
> +
> + mutex_lock(&pb->mii_bus->mdio_lock);
> + r = pb->switch_fn(pb->current_child, cb->bus_number, pb->switch_data);
> + if (r)
> + goto out;
> +
> + pb->current_child = cb->bus_number;
> +
> + r = pb->mii_bus->write(pb->mii_bus, phy_id, regnum, val);
> +out:
> + mutex_unlock(&pb->mii_bus->mdio_lock);
> +
> + return r;
> +}
> +
> +static int parent_count;
> +
> +int mdio_mux_probe(struct platform_device *pdev,
> + int (*switch_fn)(int cur, int desired, void *data),
> + void *data)
> +{
> + struct device_node *parent_bus_node;
> + struct device_node *child_bus_node;
> + int r, n, ret_val;
> + struct mii_bus *parent_bus;
> + struct mdio_mux_parent_bus *pb;
> + struct mdio_mux_child_bus *cb;
> +
> + if (!pdev->dev.of_node)
> + return -ENODEV;
> +
> + parent_bus_node = of_parse_phandle(pdev->dev.of_node, "parent-bus", 0);
> +
> + if (!parent_bus_node)
> + return -ENODEV;
> +
> + parent_bus = of_mdio_find_bus(parent_bus_node);
So what happens if the parent bus probe happens after the mux probe?
> +
> + pb = devm_kzalloc(&pdev->dev, sizeof(*pb), GFP_KERNEL);
> + if (pb == NULL) {
> + ret_val = -ENOMEM;
> + goto err_parent_bus;
> + }
> +
> + pb->switch_data = data;
> + pb->switch_fn = switch_fn;
> + pb->current_child = -1;
> + pb->parent_id = parent_count++;
> + pb->mii_bus = parent_bus;
> +
> + n = 0;
> + for_each_child_of_node(pdev->dev.of_node, child_bus_node) {
> + u32 v;
> +
> + r = of_property_read_u32(child_bus_node, "cell-index", &v);
> + if (r == 0) {
> + cb = devm_kzalloc(&pdev->dev, sizeof(*cb), GFP_KERNEL);
> + if (cb == NULL)
> + break;
> + cb->bus_number = v;
> + cb->parent = pb;
> + cb->mii_bus = mdiobus_alloc();
> + cb->mii_bus->priv = cb;
> +
> + cb->mii_bus->irq = cb->phy_irq;
> + cb->mii_bus->name = "mdio_mux";
> + snprintf(cb->mii_bus->id, MII_BUS_ID_SIZE, "%x.%x",
> + pb->parent_id, v);
> + cb->mii_bus->parent = &pdev->dev;
> + cb->mii_bus->read = mdio_mux_read;
> + cb->mii_bus->write = mdio_mux_write;
> + r = of_mdiobus_register(cb->mii_bus, child_bus_node);
> + if (r) {
> + of_node_put(child_bus_node);
> + devm_kfree(&pdev->dev, cb);
> + } else {
> + n++;
> + }
> +
> + } else {
> + of_node_put(child_bus_node);
> + }
> + }
> + if (n) {
> + dev_info(&pdev->dev, "Version " DRV_VERSION "\n");
> + return 0;
> + }
> + ret_val = -ENOMEM;
> + devm_kfree(&pdev->dev, pb);
> +err_parent_bus:
> + of_node_put(parent_bus_node);
> + return ret_val;
> +}
> +EXPORT_SYMBOL(mdio_mux_probe);
> +
> +static int __devexit mdio_mux_remove(struct platform_device *pdev)
> +{
> + return 0;
> +}
> +
> +static int __init mdio_mux_mod_init(void)
> +{
> + return 0;
> +}
> +module_init(mdio_mux_mod_init);
> +
> +static void __exit mdio_mux_mod_exit(void)
> +{
> +}
> +module_exit(mdio_mux_mod_exit);
> +
> +MODULE_DESCRIPTION(DRV_DESCRIPTION);
> +MODULE_VERSION(DRV_VERSION);
> +MODULE_AUTHOR("David Daney");
> +MODULE_LICENSE("GPL");
