drivers/net/mdio/mdio-i2c.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * MDIO I2C bridge
  *
  * Copyright (C) 2015-2016 Russell King
  * Copyright (C) 2021 Marek Behun
  *
  * Network PHYs can appear on I2C buses when they are part of SFP module.
  * This driver exposes these PHYs to the networking PHY code, allowing
  * our PHY drivers access to these PHYs, and so allowing configuration
  * of their settings.
  */
 #include <linux/i2c.h>
 #include <linux/mdio/mdio-i2c.h>
 #include <linux/phy.h>
 #include <linux/sfp.h>

 /*
  * I2C bus addresses 0x50 and 0x51 are normally an EEPROM, which is
  * specified to be present in SFP modules.  These correspond with PHY
  * addresses 16 and 17.  Disallow access to these "phy" addresses.
  */
 static bool i2c_mii_valid_phy_id(int phy_id)
 {
 	return phy_id != 0x10 && phy_id != 0x11;
 }

 static unsigned int i2c_mii_phy_addr(int phy_id)
 {
 	return phy_id + 0x40;
 }

 static int i2c_mii_read_default_c45(struct mii_bus *bus, int phy_id, int devad,
 				    int reg)
 {
 	struct i2c_adapter *i2c = bus->priv;
 	struct i2c_msg msgs[2];
 	u8 addr[3], data[2], *p;
 	int bus_addr, ret;

 	if (!i2c_mii_valid_phy_id(phy_id))
 		return 0xffff;

 	p = addr;
 	if (devad >= 0) {
 		*p++ = 0x20 | devad;
 		*p++ = reg >> 8;
 	}
 	*p++ = reg;

 	bus_addr = i2c_mii_phy_addr(phy_id);
 	msgs[0].addr = bus_addr;
 	msgs[0].flags = 0;
 	msgs[0].len = p - addr;
 	msgs[0].buf = addr;
 	msgs[1].addr = bus_addr;
 	msgs[1].flags = I2C_M_RD;
 	msgs[1].len = sizeof(data);
 	msgs[1].buf = data;

 	ret = i2c_transfer(i2c, msgs, ARRAY_SIZE(msgs));
 	if (ret != ARRAY_SIZE(msgs))
 		return 0xffff;

 	return data[0] << 8 | data[1];
 }

 static int i2c_mii_write_default_c45(struct mii_bus *bus, int phy_id,
 				     int devad, int reg, u16 val)
 {
 	struct i2c_adapter *i2c = bus->priv;
 	struct i2c_msg msg;
 	int ret;
 	u8 data[5], *p;

 	if (!i2c_mii_valid_phy_id(phy_id))
 		return 0;

 	p = data;
 	if (devad >= 0) {
 		*p++ = devad;
 		*p++ = reg >> 8;
 	}
 	*p++ = reg;
 	*p++ = val >> 8;
 	*p++ = val;

 	msg.addr = i2c_mii_phy_addr(phy_id);
 	msg.flags = 0;
 	msg.len = p - data;
 	msg.buf = data;

 	ret = i2c_transfer(i2c, &msg, 1);

 	return ret < 0 ? ret : 0;
 }

 static int i2c_mii_read_default_c22(struct mii_bus *bus, int phy_id, int reg)
 {
 	return i2c_mii_read_default_c45(bus, phy_id, -1, reg);
 }

 static int i2c_mii_write_default_c22(struct mii_bus *bus, int phy_id, int reg,
 				     u16 val)
 {
 	return i2c_mii_write_default_c45(bus, phy_id, -1, reg, val);
 }

 /* RollBall SFPs do not access internal PHY via I2C address 0x56, but
  * instead via address 0x51, when SFP page is set to 0x03 and password to
  * 0xffffffff.
  *
  * address  size  contents  description
  * -------  ----  --------  -----------
  * 0x80     1     CMD       0x01/0x02/0x04 for write/read/done
  * 0x81     1     DEV       Clause 45 device
  * 0x82     2     REG       Clause 45 register
  * 0x84     2     VAL       Register value
  */
 #define ROLLBALL_PHY_I2C_ADDR		0x51

 #define ROLLBALL_PASSWORD		(SFP_VSL + 3)

 #define ROLLBALL_CMD_ADDR		0x80
 #define ROLLBALL_DATA_ADDR		0x81

 #define ROLLBALL_CMD_WRITE		0x01
 #define ROLLBALL_CMD_READ		0x02
 #define ROLLBALL_CMD_DONE		0x04

 #define SFP_PAGE_ROLLBALL_MDIO		3

 static int __i2c_transfer_err(struct i2c_adapter *i2c, struct i2c_msg *msgs,
 			      int num)
 {
 	int ret;

 	ret = __i2c_transfer(i2c, msgs, num);
 	if (ret < 0)
 		return ret;
 	else if (ret != num)
 		return -EIO;
 	else
 		return 0;
 }

 static int __i2c_rollball_get_page(struct i2c_adapter *i2c, int bus_addr,
 				   u8 *page)
 {
 	struct i2c_msg msgs[2];
 	u8 addr = SFP_PAGE;

 	msgs[0].addr = bus_addr;
 	msgs[0].flags = 0;
 	msgs[0].len = 1;
 	msgs[0].buf = &addr;

 	msgs[1].addr = bus_addr;
 	msgs[1].flags = I2C_M_RD;
 	msgs[1].len = 1;
 	msgs[1].buf = page;

 	return __i2c_transfer_err(i2c, msgs, 2);
 }

 static int __i2c_rollball_set_page(struct i2c_adapter *i2c, int bus_addr,
 				   u8 page)
 {
 	struct i2c_msg msg;
 	u8 buf[2];

 	buf[0] = SFP_PAGE;
 	buf[1] = page;

 	msg.addr = bus_addr;
 	msg.flags = 0;
 	msg.len = 2;
 	msg.buf = buf;

 	return __i2c_transfer_err(i2c, &msg, 1);
 }

 /* In order to not interfere with other SFP code (which possibly may manipulate
  * SFP_PAGE), for every transfer we do this:
  *   1. lock the bus
  *   2. save content of SFP_PAGE
  *   3. set SFP_PAGE to 3
  *   4. do the transfer
  *   5. restore original SFP_PAGE
  *   6. unlock the bus
  * Note that one might think that steps 2 to 5 could be theoretically done all
  * in one call to i2c_transfer (by constructing msgs array in such a way), but
  * unfortunately tests show that this does not work :-( Changed SFP_PAGE does
  * not take into account until i2c_transfer() is done.
  */
 static int i2c_transfer_rollball(struct i2c_adapter *i2c,
 				 struct i2c_msg *msgs, int num)
 {
 	int ret, main_err = 0;
 	u8 saved_page;

 	i2c_lock_bus(i2c, I2C_LOCK_SEGMENT);

 	/* save original page */
 	ret = __i2c_rollball_get_page(i2c, msgs->addr, &saved_page);
 	if (ret)
 		goto unlock;

 	/* change to RollBall MDIO page */
 	ret = __i2c_rollball_set_page(i2c, msgs->addr, SFP_PAGE_ROLLBALL_MDIO);
 	if (ret)
 		goto unlock;

 	/* do the transfer; we try to restore original page if this fails */
 	ret = __i2c_transfer_err(i2c, msgs, num);
 	if (ret)
 		main_err = ret;

 	/* restore original page */
 	ret = __i2c_rollball_set_page(i2c, msgs->addr, saved_page);

 unlock:
 	i2c_unlock_bus(i2c, I2C_LOCK_SEGMENT);

 	return main_err ? : ret;
 }

 static int i2c_rollball_mii_poll(struct mii_bus *bus, int bus_addr, u8 *buf,
 				 size_t len)
 {
 	struct i2c_adapter *i2c = bus->priv;
 	struct i2c_msg msgs[2];
 	u8 cmd_addr, tmp, *res;
 	int i, ret;

 	cmd_addr = ROLLBALL_CMD_ADDR;

 	res = buf ? buf : &tmp;
 	len = buf ? len : 1;

 	msgs[0].addr = bus_addr;
 	msgs[0].flags = 0;
 	msgs[0].len = 1;
 	msgs[0].buf = &cmd_addr;

 	msgs[1].addr = bus_addr;
 	msgs[1].flags = I2C_M_RD;
 	msgs[1].len = len;
 	msgs[1].buf = res;

 	/* By experiment it takes up to 70 ms to access a register for these
 	 * SFPs. Sleep 20ms between iterations and try 10 times.
 	 */
 	i = 10;
 	do {
 		msleep(20);

 		ret = i2c_transfer_rollball(i2c, msgs, ARRAY_SIZE(msgs));
 		if (ret)
 			return ret;

 		if (*res == ROLLBALL_CMD_DONE)
 			return 0;
 	} while (i-- > 0);

 	dev_dbg(&bus->dev, "poll timed out\n");

 	return -ETIMEDOUT;
 }

 static int i2c_rollball_mii_cmd(struct mii_bus *bus, int bus_addr, u8 cmd,
 				u8 *data, size_t len)
 {
 	struct i2c_adapter *i2c = bus->priv;
 	struct i2c_msg msgs[2];
 	u8 cmdbuf[2];

 	cmdbuf[0] = ROLLBALL_CMD_ADDR;
 	cmdbuf[1] = cmd;

 	msgs[0].addr = bus_addr;
 	msgs[0].flags = 0;
 	msgs[0].len = len;
 	msgs[0].buf = data;

 	msgs[1].addr = bus_addr;
 	msgs[1].flags = 0;
 	msgs[1].len = sizeof(cmdbuf);
 	msgs[1].buf = cmdbuf;

 	return i2c_transfer_rollball(i2c, msgs, ARRAY_SIZE(msgs));
 }

 static int i2c_mii_read_rollball(struct mii_bus *bus, int phy_id, int devad,
 				 int reg)
 {
 	u8 buf[4], res[6];
 	int bus_addr, ret;
 	u16 val;

 	bus_addr = i2c_mii_phy_addr(phy_id);
 	if (bus_addr != ROLLBALL_PHY_I2C_ADDR)
 		return 0xffff;

 	buf[0] = ROLLBALL_DATA_ADDR;
 	buf[1] = devad;
 	buf[2] = (reg >> 8) & 0xff;
 	buf[3] = reg & 0xff;

 	ret = i2c_rollball_mii_cmd(bus, bus_addr, ROLLBALL_CMD_READ, buf,
 				   sizeof(buf));
 	if (ret < 0)
 		return ret;

 	ret = i2c_rollball_mii_poll(bus, bus_addr, res, sizeof(res));
 	if (ret == -ETIMEDOUT)
 		return 0xffff;
 	else if (ret < 0)
 		return ret;

 	val = res[4] << 8 | res[5];

 	return val;
 }

 static int i2c_mii_write_rollball(struct mii_bus *bus, int phy_id, int devad,
 				  int reg, u16 val)
 {
 	int bus_addr, ret;
 	u8 buf[6];

 	bus_addr = i2c_mii_phy_addr(phy_id);
 	if (bus_addr != ROLLBALL_PHY_I2C_ADDR)
 		return 0;

 	buf[0] = ROLLBALL_DATA_ADDR;
 	buf[1] = devad;
 	buf[2] = (reg >> 8) & 0xff;
 	buf[3] = reg & 0xff;
 	buf[4] = val >> 8;
 	buf[5] = val & 0xff;

 	ret = i2c_rollball_mii_cmd(bus, bus_addr, ROLLBALL_CMD_WRITE, buf,
 				   sizeof(buf));
 	if (ret < 0)
 		return ret;

 	ret = i2c_rollball_mii_poll(bus, bus_addr, NULL, 0);
 	if (ret < 0)
 		return ret;

 	return 0;
 }

 static int i2c_mii_init_rollball(struct i2c_adapter *i2c)
 {
 	struct i2c_msg msg;
 	u8 pw[5];
 	int ret;

 	pw[0] = ROLLBALL_PASSWORD;
 	pw[1] = 0xff;
 	pw[2] = 0xff;
 	pw[3] = 0xff;
 	pw[4] = 0xff;

 	msg.addr = ROLLBALL_PHY_I2C_ADDR;
 	msg.flags = 0;
 	msg.len = sizeof(pw);
 	msg.buf = pw;

 	ret = i2c_transfer(i2c, &msg, 1);
 	if (ret < 0)
 		return ret;
 	else if (ret != 1)
 		return -EIO;
 	else
 		return 0;
 }

 struct mii_bus *mdio_i2c_alloc(struct device *parent, struct i2c_adapter *i2c,
 			       enum mdio_i2c_proto protocol)
 {
 	struct mii_bus *mii;
 	int ret;

 	if (!i2c_check_functionality(i2c, I2C_FUNC_I2C))
 		return ERR_PTR(-EINVAL);

 	mii = mdiobus_alloc();
 	if (!mii)
 		return ERR_PTR(-ENOMEM);

 	snprintf(mii->id, MII_BUS_ID_SIZE, "i2c:%s", dev_name(parent));
 	mii->parent = parent;
 	mii->priv = i2c;

 	switch (protocol) {
 	case MDIO_I2C_ROLLBALL:
 		ret = i2c_mii_init_rollball(i2c);
 		if (ret < 0) {
 			dev_err(parent,
 				"Cannot initialize RollBall MDIO I2C protocol: %d\n",
 				ret);
 			mdiobus_free(mii);
 			return ERR_PTR(ret);
 		}

 		mii->read_c45 = i2c_mii_read_rollball;
 		mii->write_c45 = i2c_mii_write_rollball;
 		break;
 	default:
 		mii->read = i2c_mii_read_default_c22;
 		mii->write = i2c_mii_write_default_c22;
 		mii->read_c45 = i2c_mii_read_default_c45;
 		mii->write_c45 = i2c_mii_write_default_c45;
 		break;
 	}

 	return mii;
 }
 EXPORT_SYMBOL_GPL(mdio_i2c_alloc);

 MODULE_AUTHOR("Russell King");
 MODULE_DESCRIPTION("MDIO I2C bridge library");
 MODULE_LICENSE("GPL v2");
	// SPDX-License-Identifier: GPL-2.0
	/*
	* MDIO I2C bridge
	*
	* Copyright (C) 2015-2016 Russell King
	* Copyright (C) 2021 Marek Behun
	*
	* Network PHYs can appear on I2C buses when they are part of SFP module.
	* This driver exposes these PHYs to the networking PHY code, allowing
	* our PHY drivers access to these PHYs, and so allowing configuration
	* of their settings.
	*/
	#include <linux/i2c.h>
	#include <linux/mdio/mdio-i2c.h>
	#include <linux/phy.h>
	#include <linux/sfp.h>

	/*
	* I2C bus addresses 0x50 and 0x51 are normally an EEPROM, which is
	* specified to be present in SFP modules. These correspond with PHY
	* addresses 16 and 17. Disallow access to these "phy" addresses.
	*/
	static bool i2c_mii_valid_phy_id(int phy_id)
	{
	return phy_id != 0x10 && phy_id != 0x11;
	}

	static unsigned int i2c_mii_phy_addr(int phy_id)
	{
	return phy_id + 0x40;
	}

	static int i2c_mii_read_default_c45(struct mii_bus *bus, int phy_id, int devad,
	int reg)
	{
	struct i2c_adapter *i2c = bus->priv;
	struct i2c_msg msgs[2];
	u8 addr[3], data[2], *p;
	int bus_addr, ret;

	if (!i2c_mii_valid_phy_id(phy_id))
	return 0xffff;

	p = addr;
	if (devad >= 0) {
	*p++ = 0x20 \| devad;
	*p++ = reg >> 8;
	}
	*p++ = reg;

	bus_addr = i2c_mii_phy_addr(phy_id);
	msgs[0].addr = bus_addr;
	msgs[0].flags = 0;
	msgs[0].len = p - addr;
	msgs[0].buf = addr;
	msgs[1].addr = bus_addr;
	msgs[1].flags = I2C_M_RD;
	msgs[1].len = sizeof(data);
	msgs[1].buf = data;

	ret = i2c_transfer(i2c, msgs, ARRAY_SIZE(msgs));
	if (ret != ARRAY_SIZE(msgs))
	return 0xffff;

	return data[0] << 8 \| data[1];
	}

	static int i2c_mii_write_default_c45(struct mii_bus *bus, int phy_id,
	int devad, int reg, u16 val)
	{
	struct i2c_adapter *i2c = bus->priv;
	struct i2c_msg msg;
	int ret;
	u8 data[5], *p;

	if (!i2c_mii_valid_phy_id(phy_id))
	return 0;

	p = data;
	if (devad >= 0) {
	*p++ = devad;
	*p++ = reg >> 8;
	}
	*p++ = reg;
	*p++ = val >> 8;
	*p++ = val;

	msg.addr = i2c_mii_phy_addr(phy_id);
	msg.flags = 0;
	msg.len = p - data;
	msg.buf = data;

	ret = i2c_transfer(i2c, &msg, 1);

	return ret < 0 ? ret : 0;
	}

	static int i2c_mii_read_default_c22(struct mii_bus *bus, int phy_id, int reg)
	{
	return i2c_mii_read_default_c45(bus, phy_id, -1, reg);
	}

	static int i2c_mii_write_default_c22(struct mii_bus *bus, int phy_id, int reg,
	u16 val)
	{
	return i2c_mii_write_default_c45(bus, phy_id, -1, reg, val);
	}

	/* RollBall SFPs do not access internal PHY via I2C address 0x56, but
	* instead via address 0x51, when SFP page is set to 0x03 and password to
	* 0xffffffff.
	*
	* address size contents description
	* ------- ---- -------- -----------
	* 0x80 1 CMD 0x01/0x02/0x04 for write/read/done
	* 0x81 1 DEV Clause 45 device
	* 0x82 2 REG Clause 45 register
	* 0x84 2 VAL Register value
	*/
	#define ROLLBALL_PHY_I2C_ADDR 0x51

	#define ROLLBALL_PASSWORD (SFP_VSL + 3)

	#define ROLLBALL_CMD_ADDR 0x80
	#define ROLLBALL_DATA_ADDR 0x81

	#define ROLLBALL_CMD_WRITE 0x01
	#define ROLLBALL_CMD_READ 0x02
	#define ROLLBALL_CMD_DONE 0x04

	#define SFP_PAGE_ROLLBALL_MDIO 3

	static int __i2c_transfer_err(struct i2c_adapter i2c, struct i2c_msg msgs,
	int num)
	{
	int ret;

	ret = __i2c_transfer(i2c, msgs, num);
	if (ret < 0)
	return ret;
	else if (ret != num)
	return -EIO;
	else
	return 0;
	}

	static int __i2c_rollball_get_page(struct i2c_adapter *i2c, int bus_addr,
	u8 *page)
	{
	struct i2c_msg msgs[2];
	u8 addr = SFP_PAGE;

	msgs[0].addr = bus_addr;
	msgs[0].flags = 0;
	msgs[0].len = 1;
	msgs[0].buf = &addr;

	msgs[1].addr = bus_addr;
	msgs[1].flags = I2C_M_RD;
	msgs[1].len = 1;
	msgs[1].buf = page;

	return __i2c_transfer_err(i2c, msgs, 2);
	}

	static int __i2c_rollball_set_page(struct i2c_adapter *i2c, int bus_addr,
	u8 page)
	{
	struct i2c_msg msg;
	u8 buf[2];

	buf[0] = SFP_PAGE;
	buf[1] = page;

	msg.addr = bus_addr;
	msg.flags = 0;
	msg.len = 2;
	msg.buf = buf;

	return __i2c_transfer_err(i2c, &msg, 1);
	}

	/* In order to not interfere with other SFP code (which possibly may manipulate
	* SFP_PAGE), for every transfer we do this:
	* 1. lock the bus
	* 2. save content of SFP_PAGE
	* 3. set SFP_PAGE to 3
	* 4. do the transfer
	* 5. restore original SFP_PAGE
	* 6. unlock the bus
	* Note that one might think that steps 2 to 5 could be theoretically done all
	* in one call to i2c_transfer (by constructing msgs array in such a way), but
	* unfortunately tests show that this does not work :-( Changed SFP_PAGE does
	* not take into account until i2c_transfer() is done.
	*/
	static int i2c_transfer_rollball(struct i2c_adapter *i2c,
	struct i2c_msg *msgs, int num)
	{
	int ret, main_err = 0;
	u8 saved_page;

	i2c_lock_bus(i2c, I2C_LOCK_SEGMENT);

	/* save original page */
	ret = __i2c_rollball_get_page(i2c, msgs->addr, &saved_page);
	if (ret)
	goto unlock;

	/* change to RollBall MDIO page */
	ret = __i2c_rollball_set_page(i2c, msgs->addr, SFP_PAGE_ROLLBALL_MDIO);
	if (ret)
	goto unlock;

	/* do the transfer; we try to restore original page if this fails */
	ret = __i2c_transfer_err(i2c, msgs, num);
	if (ret)
	main_err = ret;

	/* restore original page */
	ret = __i2c_rollball_set_page(i2c, msgs->addr, saved_page);

	unlock:
	i2c_unlock_bus(i2c, I2C_LOCK_SEGMENT);

	return main_err ? : ret;
	}

	static int i2c_rollball_mii_poll(struct mii_bus bus, int bus_addr, u8 buf,
	size_t len)
	{
	struct i2c_adapter *i2c = bus->priv;
	struct i2c_msg msgs[2];
	u8 cmd_addr, tmp, *res;
	int i, ret;

	cmd_addr = ROLLBALL_CMD_ADDR;

	res = buf ? buf : &tmp;
	len = buf ? len : 1;

	msgs[0].addr = bus_addr;
	msgs[0].flags = 0;
	msgs[0].len = 1;
	msgs[0].buf = &cmd_addr;

	msgs[1].addr = bus_addr;
	msgs[1].flags = I2C_M_RD;
	msgs[1].len = len;
	msgs[1].buf = res;

	/* By experiment it takes up to 70 ms to access a register for these
	* SFPs. Sleep 20ms between iterations and try 10 times.
	*/
	i = 10;
	do {
	msleep(20);

	ret = i2c_transfer_rollball(i2c, msgs, ARRAY_SIZE(msgs));
	if (ret)
	return ret;

	if (*res == ROLLBALL_CMD_DONE)
	return 0;
	} while (i-- > 0);

	dev_dbg(&bus->dev, "poll timed out\n");

	return -ETIMEDOUT;
	}

	static int i2c_rollball_mii_cmd(struct mii_bus *bus, int bus_addr, u8 cmd,
	u8 *data, size_t len)
	{
	struct i2c_adapter *i2c = bus->priv;
	struct i2c_msg msgs[2];
	u8 cmdbuf[2];

	cmdbuf[0] = ROLLBALL_CMD_ADDR;
	cmdbuf[1] = cmd;

	msgs[0].addr = bus_addr;
	msgs[0].flags = 0;
	msgs[0].len = len;
	msgs[0].buf = data;

	msgs[1].addr = bus_addr;
	msgs[1].flags = 0;
	msgs[1].len = sizeof(cmdbuf);
	msgs[1].buf = cmdbuf;

	return i2c_transfer_rollball(i2c, msgs, ARRAY_SIZE(msgs));
	}

	static int i2c_mii_read_rollball(struct mii_bus *bus, int phy_id, int devad,
	int reg)
	{
	u8 buf[4], res[6];
	int bus_addr, ret;
	u16 val;

	bus_addr = i2c_mii_phy_addr(phy_id);
	if (bus_addr != ROLLBALL_PHY_I2C_ADDR)
	return 0xffff;

	buf[0] = ROLLBALL_DATA_ADDR;
	buf[1] = devad;
	buf[2] = (reg >> 8) & 0xff;
	buf[3] = reg & 0xff;

	ret = i2c_rollball_mii_cmd(bus, bus_addr, ROLLBALL_CMD_READ, buf,
	sizeof(buf));
	if (ret < 0)
	return ret;

	ret = i2c_rollball_mii_poll(bus, bus_addr, res, sizeof(res));
	if (ret == -ETIMEDOUT)
	return 0xffff;
	else if (ret < 0)
	return ret;

	val = res[4] << 8 \| res[5];

	return val;
	}

	static int i2c_mii_write_rollball(struct mii_bus *bus, int phy_id, int devad,
	int reg, u16 val)
	{
	int bus_addr, ret;
	u8 buf[6];

	bus_addr = i2c_mii_phy_addr(phy_id);
	if (bus_addr != ROLLBALL_PHY_I2C_ADDR)
	return 0;

	buf[0] = ROLLBALL_DATA_ADDR;
	buf[1] = devad;
	buf[2] = (reg >> 8) & 0xff;
	buf[3] = reg & 0xff;
	buf[4] = val >> 8;
	buf[5] = val & 0xff;

	ret = i2c_rollball_mii_cmd(bus, bus_addr, ROLLBALL_CMD_WRITE, buf,
	sizeof(buf));
	if (ret < 0)
	return ret;

	ret = i2c_rollball_mii_poll(bus, bus_addr, NULL, 0);
	if (ret < 0)
	return ret;

	return 0;
	}

	static int i2c_mii_init_rollball(struct i2c_adapter *i2c)
	{
	struct i2c_msg msg;
	u8 pw[5];
	int ret;

	pw[0] = ROLLBALL_PASSWORD;
	pw[1] = 0xff;
	pw[2] = 0xff;
	pw[3] = 0xff;
	pw[4] = 0xff;

	msg.addr = ROLLBALL_PHY_I2C_ADDR;
	msg.flags = 0;
	msg.len = sizeof(pw);
	msg.buf = pw;

	ret = i2c_transfer(i2c, &msg, 1);
	if (ret < 0)
	return ret;
	else if (ret != 1)
	return -EIO;
	else
	return 0;
	}

	struct mii_bus mdio_i2c_alloc(struct device parent, struct i2c_adapter *i2c,
	enum mdio_i2c_proto protocol)
	{
	struct mii_bus *mii;
	int ret;

	if (!i2c_check_functionality(i2c, I2C_FUNC_I2C))
	return ERR_PTR(-EINVAL);

	mii = mdiobus_alloc();
	if (!mii)
	return ERR_PTR(-ENOMEM);

	snprintf(mii->id, MII_BUS_ID_SIZE, "i2c:%s", dev_name(parent));
	mii->parent = parent;
	mii->priv = i2c;

	switch (protocol) {
	case MDIO_I2C_ROLLBALL:
	ret = i2c_mii_init_rollball(i2c);
	if (ret < 0) {
	dev_err(parent,
	"Cannot initialize RollBall MDIO I2C protocol: %d\n",
	ret);
	mdiobus_free(mii);
	return ERR_PTR(ret);
	}

	mii->read_c45 = i2c_mii_read_rollball;
	mii->write_c45 = i2c_mii_write_rollball;
	break;
	default:
	mii->read = i2c_mii_read_default_c22;
	mii->write = i2c_mii_write_default_c22;
	mii->read_c45 = i2c_mii_read_default_c45;
	mii->write_c45 = i2c_mii_write_default_c45;
	break;
	}

	return mii;
	}
	EXPORT_SYMBOL_GPL(mdio_i2c_alloc);

	MODULE_AUTHOR("Russell King");
	MODULE_DESCRIPTION("MDIO I2C bridge library");
	MODULE_LICENSE("GPL v2");