/*
   * I2C multiplexer driver for PCA9541 bus master selector
   *
   * Copyright (c) 2010 Ericsson AB.
   *
   * Author: Guenter Roeck <linux@roeck-us.net>
   *
   * 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/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 = dev_get_platdata(&client->dev);
  	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
  ");
  		goto exit_free;
  	}
  
  	dev_info(&client->dev, "registered master selector for I2C %s
  ",
  		 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");