drivers/i2c/muxes/i2c-mux-pca9541.c - kernel/msm-4.19 - Gitiles

 /*
  * I2C multiplexer driver for PCA9541 bus master selector
  *
  * Copyright (c) 2010 Ericsson AB.
  *
  * Author: Guenter Roeck <guenter.roeck@ericsson.com>
  *
  * Derived from:
  *  pca954x.c
  *
  *  Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it>
  *  Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it>
  *
  * This file is licensed under the terms of the GNU General Public
  * License version 2. This program is licensed "as is" without any
  * warranty of any kind, whether express or implied.
  */

 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/jiffies.h>
 #include <linux/delay.h>
 #include <linux/slab.h>
 #include <linux/device.h>
 #include <linux/i2c.h>
 #include <linux/i2c-mux.h>

 #include <linux/i2c/pca954x.h>

 /*
  * The PCA9541 is a bus master selector. It supports two I2C masters connected
  * to a single slave bus.
  *
  * Before each bus transaction, a master has to acquire bus ownership. After the
  * transaction is complete, bus ownership has to be released. This fits well
  * into the I2C multiplexer framework, which provides select and release
  * functions for this purpose. For this reason, this driver is modeled as
  * single-channel I2C bus multiplexer.
  *
  * This driver assumes that the two bus masters are controlled by two different
  * hosts. If a single host controls both masters, platform code has to ensure
  * that only one of the masters is instantiated at any given time.
  */

 #define PCA9541_CONTROL		0x01
 #define PCA9541_ISTAT		0x02

 #define PCA9541_CTL_MYBUS	(1 << 0)
 #define PCA9541_CTL_NMYBUS	(1 << 1)
 #define PCA9541_CTL_BUSON	(1 << 2)
 #define PCA9541_CTL_NBUSON	(1 << 3)
 #define PCA9541_CTL_BUSINIT	(1 << 4)
 #define PCA9541_CTL_TESTON	(1 << 6)
 #define PCA9541_CTL_NTESTON	(1 << 7)

 #define PCA9541_ISTAT_INTIN	(1 << 0)
 #define PCA9541_ISTAT_BUSINIT	(1 << 1)
 #define PCA9541_ISTAT_BUSOK	(1 << 2)
 #define PCA9541_ISTAT_BUSLOST	(1 << 3)
 #define PCA9541_ISTAT_MYTEST	(1 << 6)
 #define PCA9541_ISTAT_NMYTEST	(1 << 7)

 #define BUSON		(PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON)
 #define MYBUS		(PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS)
 #define mybus(x)	(!((x) & MYBUS) || ((x) & MYBUS) == MYBUS)
 #define busoff(x)	(!((x) & BUSON) || ((x) & BUSON) == BUSON)

 /* arbitration timeouts, in jiffies */
 #define ARB_TIMEOUT	(HZ / 8)	/* 125 ms until forcing bus ownership */
 #define ARB2_TIMEOUT	(HZ / 4)	/* 250 ms until acquisition failure */

 /* arbitration retry delays, in us */
 #define SELECT_DELAY_SHORT	50
 #define SELECT_DELAY_LONG	1000

 struct pca9541 {
 	struct i2c_adapter *mux_adap;
 	unsigned long select_timeout;
 	unsigned long arb_timeout;
 };

 static const struct i2c_device_id pca9541_id[] = {
 	{"pca9541", 0},
 	{}
 };

 MODULE_DEVICE_TABLE(i2c, pca9541_id);

 /*
  * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
  * as they will try to lock the adapter a second time.
  */
 static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
 {
 	struct i2c_adapter *adap = client->adapter;
 	int ret;

 	if (adap->algo->master_xfer) {
 		struct i2c_msg msg;
 		char buf[2];

 		msg.addr = client->addr;
 		msg.flags = 0;
 		msg.len = 2;
 		buf[0] = command;
 		buf[1] = val;
 		msg.buf = buf;
 		ret = adap->algo->master_xfer(adap, &msg, 1);
 	} else {
 		union i2c_smbus_data data;

 		data.byte = val;
 		ret = adap->algo->smbus_xfer(adap, client->addr,
 					     client->flags,
 					     I2C_SMBUS_WRITE,
 					     command,
 					     I2C_SMBUS_BYTE_DATA, &data);
 	}

 	return ret;
 }

 /*
  * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
  * as they will try to lock adapter a second time.
  */
 static int pca9541_reg_read(struct i2c_client *client, u8 command)
 {
 	struct i2c_adapter *adap = client->adapter;
 	int ret;
 	u8 val;

 	if (adap->algo->master_xfer) {
 		struct i2c_msg msg[2] = {
 			{
 				.addr = client->addr,
 				.flags = 0,
 				.len = 1,
 				.buf = &command
 			},
 			{
 				.addr = client->addr,
 				.flags = I2C_M_RD,
 				.len = 1,
 				.buf = &val
 			}
 		};
 		ret = adap->algo->master_xfer(adap, msg, 2);
 		if (ret == 2)
 			ret = val;
 		else if (ret >= 0)
 			ret = -EIO;
 	} else {
 		union i2c_smbus_data data;

 		ret = adap->algo->smbus_xfer(adap, client->addr,
 					     client->flags,
 					     I2C_SMBUS_READ,
 					     command,
 					     I2C_SMBUS_BYTE_DATA, &data);
 		if (!ret)
 			ret = data.byte;
 	}
 	return ret;
 }

 /*
  * Arbitration management functions
  */

 /* Release bus. Also reset NTESTON and BUSINIT if it was set. */
 static void pca9541_release_bus(struct i2c_client *client)
 {
 	int reg;

 	reg = pca9541_reg_read(client, PCA9541_CONTROL);
 	if (reg >= 0 && !busoff(reg) && mybus(reg))
 		pca9541_reg_write(client, PCA9541_CONTROL,
 				  (reg & PCA9541_CTL_NBUSON) >> 1);
 }

 /*
  * Arbitration is defined as a two-step process. A bus master can only activate
  * the slave bus if it owns it; otherwise it has to request ownership first.
  * This multi-step process ensures that access contention is resolved
  * gracefully.
  *
  * Bus	Ownership	Other master	Action
  * state		requested access
  * ----------------------------------------------------
  * off	-		yes		wait for arbitration timeout or
  *					for other master to drop request
  * off	no		no		take ownership
  * off	yes		no		turn on bus
  * on	yes		-		done
  * on	no		-		wait for arbitration timeout or
  *					for other master to release bus
  *
  * The main contention point occurs if the slave bus is off and both masters
  * request ownership at the same time. In this case, one master will turn on
  * the slave bus, believing that it owns it. The other master will request
  * bus ownership. Result is that the bus is turned on, and master which did
  * _not_ own the slave bus before ends up owning it.
  */

 /* Control commands per PCA9541 datasheet */
 static const u8 pca9541_control[16] = {
 	4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
 };

 /*
  * Channel arbitration
  *
  * Return values:
  *  <0: error
  *  0 : bus not acquired
  *  1 : bus acquired
  */
 static int pca9541_arbitrate(struct i2c_client *client)
 {
 	struct pca9541 *data = i2c_get_clientdata(client);
 	int reg;

 	reg = pca9541_reg_read(client, PCA9541_CONTROL);
 	if (reg < 0)
 		return reg;

 	if (busoff(reg)) {
 		int istat;
 		/*
 		 * Bus is off. Request ownership or turn it on unless
 		 * other master requested ownership.
 		 */
 		istat = pca9541_reg_read(client, PCA9541_ISTAT);
 		if (!(istat & PCA9541_ISTAT_NMYTEST)
 		    || time_is_before_eq_jiffies(data->arb_timeout)) {
 			/*
 			 * Other master did not request ownership,
 			 * or arbitration timeout expired. Take the bus.
 			 */
 			pca9541_reg_write(client,
 					  PCA9541_CONTROL,
 					  pca9541_control[reg & 0x0f]
 					  | PCA9541_CTL_NTESTON);
 			data->select_timeout = SELECT_DELAY_SHORT;
 		} else {
 			/*
 			 * Other master requested ownership.
 			 * Set extra long timeout to give it time to acquire it.
 			 */
 			data->select_timeout = SELECT_DELAY_LONG * 2;
 		}
 	} else if (mybus(reg)) {
 		/*
 		 * Bus is on, and we own it. We are done with acquisition.
 		 * Reset NTESTON and BUSINIT, then return success.
 		 */
 		if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
 			pca9541_reg_write(client,
 					  PCA9541_CONTROL,
 					  reg & ~(PCA9541_CTL_NTESTON
 						  | PCA9541_CTL_BUSINIT));
 		return 1;
 	} else {
 		/*
 		 * Other master owns the bus.
 		 * If arbitration timeout has expired, force ownership.
 		 * Otherwise request it.
 		 */
 		data->select_timeout = SELECT_DELAY_LONG;
 		if (time_is_before_eq_jiffies(data->arb_timeout)) {
 			/* Time is up, take the bus and reset it. */
 			pca9541_reg_write(client,
 					  PCA9541_CONTROL,
 					  pca9541_control[reg & 0x0f]
 					  | PCA9541_CTL_BUSINIT
 					  | PCA9541_CTL_NTESTON);
 		} else {
 			/* Request bus ownership if needed */
 			if (!(reg & PCA9541_CTL_NTESTON))
 				pca9541_reg_write(client,
 						  PCA9541_CONTROL,
 						  reg | PCA9541_CTL_NTESTON);
 		}
 	}
 	return 0;
 }

 static int pca9541_select_chan(struct i2c_adapter *adap, void *client, u32 chan)
 {
 	struct pca9541 *data = i2c_get_clientdata(client);
 	int ret;
 	unsigned long timeout = jiffies + ARB2_TIMEOUT;
 		/* give up after this time */

 	data->arb_timeout = jiffies + ARB_TIMEOUT;
 		/* force bus ownership after this time */

 	do {
 		ret = pca9541_arbitrate(client);
 		if (ret)
 			return ret < 0 ? ret : 0;

 		if (data->select_timeout == SELECT_DELAY_SHORT)
 			udelay(data->select_timeout);
 		else
 			msleep(data->select_timeout / 1000);
 	} while (time_is_after_eq_jiffies(timeout));

 	return -ETIMEDOUT;
 }

 static int pca9541_release_chan(struct i2c_adapter *adap,
 				void *client, u32 chan)
 {
 	pca9541_release_bus(client);
 	return 0;
 }

 /*
  * I2C init/probing/exit functions
  */
 static int pca9541_probe(struct i2c_client *client,
 			 const struct i2c_device_id *id)
 {
 	struct i2c_adapter *adap = client->adapter;
 	struct pca954x_platform_data *pdata = client->dev.platform_data;
 	struct pca9541 *data;
 	int force;
 	int ret = -ENODEV;

 	if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
 		goto err;

 	data = kzalloc(sizeof(struct pca9541), GFP_KERNEL);
 	if (!data) {
 		ret = -ENOMEM;
 		goto err;
 	}

 	i2c_set_clientdata(client, data);

 	/*
 	 * I2C accesses are unprotected here.
 	 * We have to lock the adapter before releasing the bus.
 	 */
 	i2c_lock_adapter(adap);
 	pca9541_release_bus(client);
 	i2c_unlock_adapter(adap);

 	/* Create mux adapter */

 	force = 0;
 	if (pdata)
 		force = pdata->modes[0].adap_id;
 	data->mux_adap = i2c_add_mux_adapter(adap, &client->dev, client,
 					     force, 0, 0,
 					     pca9541_select_chan,
 					     pca9541_release_chan);

 	if (data->mux_adap == NULL) {
 		dev_err(&client->dev, "failed to register master selector\n");
 		goto exit_free;
 	}

 	dev_info(&client->dev, "registered master selector for I2C %s\n",
 		 client->name);

 	return 0;

 exit_free:
 	kfree(data);
 err:
 	return ret;
 }

 static int pca9541_remove(struct i2c_client *client)
 {
 	struct pca9541 *data = i2c_get_clientdata(client);

 	i2c_del_mux_adapter(data->mux_adap);

 	kfree(data);
 	return 0;
 }

 static struct i2c_driver pca9541_driver = {
 	.driver = {
 		   .name = "pca9541",
 		   .owner = THIS_MODULE,
 		   },
 	.probe = pca9541_probe,
 	.remove = pca9541_remove,
 	.id_table = pca9541_id,
 };

 module_i2c_driver(pca9541_driver);

 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
 MODULE_LICENSE("GPL v2");
	/*
	* I2C multiplexer driver for PCA9541 bus master selector
	*
	* Copyright (c) 2010 Ericsson AB.
	*
	* Author: Guenter Roeck <guenter.roeck@ericsson.com>
	*
	* Derived from:
	* pca954x.c
	*
	* Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it>
	* Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it>
	*
	* This file is licensed under the terms of the GNU General Public
	* License version 2. This program is licensed "as is" without any
	* warranty of any kind, whether express or implied.
	*/

	#include <linux/module.h>
	#include <linux/init.h>
	#include <linux/jiffies.h>
	#include <linux/delay.h>
	#include <linux/slab.h>
	#include <linux/device.h>
	#include <linux/i2c.h>
	#include <linux/i2c-mux.h>

	#include <linux/i2c/pca954x.h>

	/*
	* The PCA9541 is a bus master selector. It supports two I2C masters connected
	* to a single slave bus.
	*
	* Before each bus transaction, a master has to acquire bus ownership. After the
	* transaction is complete, bus ownership has to be released. This fits well
	* into the I2C multiplexer framework, which provides select and release
	* functions for this purpose. For this reason, this driver is modeled as
	* single-channel I2C bus multiplexer.
	*
	* This driver assumes that the two bus masters are controlled by two different
	* hosts. If a single host controls both masters, platform code has to ensure
	* that only one of the masters is instantiated at any given time.
	*/

	#define PCA9541_CONTROL 0x01
	#define PCA9541_ISTAT 0x02

	#define PCA9541_CTL_MYBUS (1 << 0)
	#define PCA9541_CTL_NMYBUS (1 << 1)
	#define PCA9541_CTL_BUSON (1 << 2)
	#define PCA9541_CTL_NBUSON (1 << 3)
	#define PCA9541_CTL_BUSINIT (1 << 4)
	#define PCA9541_CTL_TESTON (1 << 6)
	#define PCA9541_CTL_NTESTON (1 << 7)

	#define PCA9541_ISTAT_INTIN (1 << 0)
	#define PCA9541_ISTAT_BUSINIT (1 << 1)
	#define PCA9541_ISTAT_BUSOK (1 << 2)
	#define PCA9541_ISTAT_BUSLOST (1 << 3)
	#define PCA9541_ISTAT_MYTEST (1 << 6)
	#define PCA9541_ISTAT_NMYTEST (1 << 7)

	#define BUSON (PCA9541_CTL_BUSON \| PCA9541_CTL_NBUSON)
	#define MYBUS (PCA9541_CTL_MYBUS \| PCA9541_CTL_NMYBUS)
	#define mybus(x) (!((x) & MYBUS) \|\| ((x) & MYBUS) == MYBUS)
	#define busoff(x) (!((x) & BUSON) \|\| ((x) & BUSON) == BUSON)

	/* arbitration timeouts, in jiffies */
	#define ARB_TIMEOUT (HZ / 8) /* 125 ms until forcing bus ownership */
	#define ARB2_TIMEOUT (HZ / 4) /* 250 ms until acquisition failure */

	/* arbitration retry delays, in us */
	#define SELECT_DELAY_SHORT 50
	#define SELECT_DELAY_LONG 1000

	struct pca9541 {
	struct i2c_adapter *mux_adap;
	unsigned long select_timeout;
	unsigned long arb_timeout;
	};

	static const struct i2c_device_id pca9541_id[] = {
	{"pca9541", 0},
	{}
	};

	MODULE_DEVICE_TABLE(i2c, pca9541_id);

	/*
	* Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
	* as they will try to lock the adapter a second time.
	*/
	static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
	{
	struct i2c_adapter *adap = client->adapter;
	int ret;

	if (adap->algo->master_xfer) {
	struct i2c_msg msg;
	char buf[2];

	msg.addr = client->addr;
	msg.flags = 0;
	msg.len = 2;
	buf[0] = command;
	buf[1] = val;
	msg.buf = buf;
	ret = adap->algo->master_xfer(adap, &msg, 1);
	} else {
	union i2c_smbus_data data;

	data.byte = val;
	ret = adap->algo->smbus_xfer(adap, client->addr,
	client->flags,
	I2C_SMBUS_WRITE,
	command,
	I2C_SMBUS_BYTE_DATA, &data);
	}

	return ret;
	}

	/*
	* Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
	* as they will try to lock adapter a second time.
	*/
	static int pca9541_reg_read(struct i2c_client *client, u8 command)
	{
	struct i2c_adapter *adap = client->adapter;
	int ret;
	u8 val;

	if (adap->algo->master_xfer) {
	struct i2c_msg msg[2] = {
	{
	.addr = client->addr,
	.flags = 0,
	.len = 1,
	.buf = &command
	},
	{
	.addr = client->addr,
	.flags = I2C_M_RD,
	.len = 1,
	.buf = &val
	}
	};
	ret = adap->algo->master_xfer(adap, msg, 2);
	if (ret == 2)
	ret = val;
	else if (ret >= 0)
	ret = -EIO;
	} else {
	union i2c_smbus_data data;

	ret = adap->algo->smbus_xfer(adap, client->addr,
	client->flags,
	I2C_SMBUS_READ,
	command,
	I2C_SMBUS_BYTE_DATA, &data);
	if (!ret)
	ret = data.byte;
	}
	return ret;
	}

	/*
	* Arbitration management functions
	*/

	/* Release bus. Also reset NTESTON and BUSINIT if it was set. */
	static void pca9541_release_bus(struct i2c_client *client)
	{
	int reg;

	reg = pca9541_reg_read(client, PCA9541_CONTROL);
	if (reg >= 0 && !busoff(reg) && mybus(reg))
	pca9541_reg_write(client, PCA9541_CONTROL,
	(reg & PCA9541_CTL_NBUSON) >> 1);
	}

	/*
	* Arbitration is defined as a two-step process. A bus master can only activate
	* the slave bus if it owns it; otherwise it has to request ownership first.
	* This multi-step process ensures that access contention is resolved
	* gracefully.
	*
	* Bus Ownership Other master Action
	* state requested access
	* ----------------------------------------------------
	* off - yes wait for arbitration timeout or
	* for other master to drop request
	* off no no take ownership
	* off yes no turn on bus
	* on yes - done
	* on no - wait for arbitration timeout or
	* for other master to release bus
	*
	* The main contention point occurs if the slave bus is off and both masters
	* request ownership at the same time. In this case, one master will turn on
	* the slave bus, believing that it owns it. The other master will request
	* bus ownership. Result is that the bus is turned on, and master which did
	* _not_ own the slave bus before ends up owning it.
	*/

	/* Control commands per PCA9541 datasheet */
	static const u8 pca9541_control[16] = {
	4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
	};

	/*
	* Channel arbitration
	*
	* Return values:
	* <0: error
	* 0 : bus not acquired
	* 1 : bus acquired
	*/
	static int pca9541_arbitrate(struct i2c_client *client)
	{
	struct pca9541 *data = i2c_get_clientdata(client);
	int reg;

	reg = pca9541_reg_read(client, PCA9541_CONTROL);
	if (reg < 0)
	return reg;

	if (busoff(reg)) {
	int istat;
	/*
	* Bus is off. Request ownership or turn it on unless
	* other master requested ownership.
	*/
	istat = pca9541_reg_read(client, PCA9541_ISTAT);
	if (!(istat & PCA9541_ISTAT_NMYTEST)
	\|\| time_is_before_eq_jiffies(data->arb_timeout)) {
	/*
	* Other master did not request ownership,
	* or arbitration timeout expired. Take the bus.
	*/
	pca9541_reg_write(client,
	PCA9541_CONTROL,
	pca9541_control[reg & 0x0f]
	\| PCA9541_CTL_NTESTON);
	data->select_timeout = SELECT_DELAY_SHORT;
	} else {
	/*
	* Other master requested ownership.
	* Set extra long timeout to give it time to acquire it.
	*/
	data->select_timeout = SELECT_DELAY_LONG * 2;
	}
	} else if (mybus(reg)) {
	/*
	* Bus is on, and we own it. We are done with acquisition.
	* Reset NTESTON and BUSINIT, then return success.
	*/
	if (reg & (PCA9541_CTL_NTESTON \| PCA9541_CTL_BUSINIT))
	pca9541_reg_write(client,
	PCA9541_CONTROL,
	reg & ~(PCA9541_CTL_NTESTON
	\| PCA9541_CTL_BUSINIT));
	return 1;
	} else {
	/*
	* Other master owns the bus.
	* If arbitration timeout has expired, force ownership.
	* Otherwise request it.
	*/
	data->select_timeout = SELECT_DELAY_LONG;
	if (time_is_before_eq_jiffies(data->arb_timeout)) {
	/* Time is up, take the bus and reset it. */
	pca9541_reg_write(client,
	PCA9541_CONTROL,
	pca9541_control[reg & 0x0f]
	\| PCA9541_CTL_BUSINIT
	\| PCA9541_CTL_NTESTON);
	} else {
	/* Request bus ownership if needed */
	if (!(reg & PCA9541_CTL_NTESTON))
	pca9541_reg_write(client,
	PCA9541_CONTROL,
	reg \| PCA9541_CTL_NTESTON);
	}
	}
	return 0;
	}

	static int pca9541_select_chan(struct i2c_adapter adap, void client, u32 chan)
	{
	struct pca9541 *data = i2c_get_clientdata(client);
	int ret;
	unsigned long timeout = jiffies + ARB2_TIMEOUT;
	/* give up after this time */

	data->arb_timeout = jiffies + ARB_TIMEOUT;
	/* force bus ownership after this time */

	do {
	ret = pca9541_arbitrate(client);
	if (ret)
	return ret < 0 ? ret : 0;

	if (data->select_timeout == SELECT_DELAY_SHORT)
	udelay(data->select_timeout);
	else
	msleep(data->select_timeout / 1000);
	} while (time_is_after_eq_jiffies(timeout));

	return -ETIMEDOUT;
	}

	static int pca9541_release_chan(struct i2c_adapter *adap,
	void *client, u32 chan)
	{
	pca9541_release_bus(client);
	return 0;
	}

	/*
	* I2C init/probing/exit functions
	*/
	static int pca9541_probe(struct i2c_client *client,
	const struct i2c_device_id *id)
	{
	struct i2c_adapter *adap = client->adapter;
	struct pca954x_platform_data *pdata = client->dev.platform_data;
	struct pca9541 *data;
	int force;
	int ret = -ENODEV;

	if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
	goto err;

	data = kzalloc(sizeof(struct pca9541), GFP_KERNEL);
	if (!data) {
	ret = -ENOMEM;
	goto err;
	}

	i2c_set_clientdata(client, data);

	/*
	* I2C accesses are unprotected here.
	* We have to lock the adapter before releasing the bus.
	*/
	i2c_lock_adapter(adap);
	pca9541_release_bus(client);
	i2c_unlock_adapter(adap);

	/* Create mux adapter */

	force = 0;
	if (pdata)
	force = pdata->modes[0].adap_id;
	data->mux_adap = i2c_add_mux_adapter(adap, &client->dev, client,
	force, 0, 0,
	pca9541_select_chan,
	pca9541_release_chan);

	if (data->mux_adap == NULL) {
	dev_err(&client->dev, "failed to register master selector\n");
	goto exit_free;
	}

	dev_info(&client->dev, "registered master selector for I2C %s\n",
	client->name);

	return 0;

	exit_free:
	kfree(data);
	err:
	return ret;
	}

	static int pca9541_remove(struct i2c_client *client)
	{
	struct pca9541 *data = i2c_get_clientdata(client);

	i2c_del_mux_adapter(data->mux_adap);

	kfree(data);
	return 0;
	}

	static struct i2c_driver pca9541_driver = {
	.driver = {
	.name = "pca9541",
	.owner = THIS_MODULE,
	},
	.probe = pca9541_probe,
	.remove = pca9541_remove,
	.id_table = pca9541_id,
	};

	module_i2c_driver(pca9541_driver);

	MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
	MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
	MODULE_LICENSE("GPL v2");