i2c-mux-pca9541.c

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/*
 * I2C multiplexer driver for PCA9541 bus master selector
 *
 * Copyright (c) 2010 Ericsson AB.
 *
 * Author: Guenter Roeck <[email protected]>
 *
 * Derived from:
 *  pca954x.c
 *
 *  Copyright (c) 2008-2009 Rodolfo Giometti <[email protected]>
 *  Copyright (c) 2008-2009 Eurotech S.p.A. <[email protected]>
 *
 * 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 <[email protected]>");
MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
MODULE_LICENSE("GPL v2");