/*
 * 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/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");