i2c-gpio.c

Go to the documentation of this file.

/*
 * Bitbanging I2C bus driver using the GPIO API
 *
 * Copyright (C) 2007 Atmel Corporation
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/i2c.h>
#include <linux/i2c-algo-bit.h>
#include <linux/i2c-gpio.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/platform_device.h>
#include <linux/gpio.h>
#include <linux/of_gpio.h>
#include <linux/of_i2c.h>

struct i2c_gpio_private_data {
    struct i2c_adapter adap;
    struct i2c_algo_bit_data bit_data;
    struct i2c_gpio_platform_data pdata;
};

/* Toggle SDA by changing the direction of the pin */
static void i2c_gpio_setsda_dir(void *data, int state)
{
    struct i2c_gpio_platform_data *pdata = data;

    if (state)
        gpio_direction_input(pdata->sda_pin);
    else
        gpio_direction_output(pdata->sda_pin, 0);
}

/*
 * Toggle SDA by changing the output value of the pin. This is only
 * valid for pins configured as open drain (i.e. setting the value
 * high effectively turns off the output driver.)
 */
static void i2c_gpio_setsda_val(void *data, int state)
{
    struct i2c_gpio_platform_data *pdata = data;

    gpio_set_value(pdata->sda_pin, state);
}

/* Toggle SCL by changing the direction of the pin. */
static void i2c_gpio_setscl_dir(void *data, int state)
{
    struct i2c_gpio_platform_data *pdata = data;

    if (state)
        gpio_direction_input(pdata->scl_pin);
    else
        gpio_direction_output(pdata->scl_pin, 0);
}

/*
 * Toggle SCL by changing the output value of the pin. This is used
 * for pins that are configured as open drain and for output-only
 * pins. The latter case will break the i2c protocol, but it will
 * often work in practice.
 */
static void i2c_gpio_setscl_val(void *data, int state)
{
    struct i2c_gpio_platform_data *pdata = data;

    gpio_set_value(pdata->scl_pin, state);
}

static int i2c_gpio_getsda(void *data)
{
    struct i2c_gpio_platform_data *pdata = data;

    return gpio_get_value(pdata->sda_pin);
}

static int i2c_gpio_getscl(void *data)
{
    struct i2c_gpio_platform_data *pdata = data;

    return gpio_get_value(pdata->scl_pin);
}

static int __devinit of_i2c_gpio_probe(struct device_node *np,
                 struct i2c_gpio_platform_data *pdata)
{
    u32 reg;

    if (of_gpio_count(np) < 2)
        return -ENODEV;

    pdata->sda_pin = of_get_gpio(np, 0);
    pdata->scl_pin = of_get_gpio(np, 1);

    if (!gpio_is_valid(pdata->sda_pin) || !gpio_is_valid(pdata->scl_pin)) {
        pr_err("%s: invalid GPIO pins, sda=%d/scl=%d\n",
               np->full_name, pdata->sda_pin, pdata->scl_pin);
        return -ENODEV;
    }

    of_property_read_u32(np, "i2c-gpio,delay-us", &pdata->udelay);

    if (!of_property_read_u32(np, "i2c-gpio,timeout-ms", &reg))
        pdata->timeout = msecs_to_jiffies(reg);

    pdata->sda_is_open_drain =
        of_property_read_bool(np, "i2c-gpio,sda-open-drain");
    pdata->scl_is_open_drain =
        of_property_read_bool(np, "i2c-gpio,scl-open-drain");
    pdata->scl_is_output_only =
        of_property_read_bool(np, "i2c-gpio,scl-output-only");

    return 0;
}

static int __devinit i2c_gpio_probe(struct platform_device *pdev)
{
    struct i2c_gpio_private_data *priv;
    struct i2c_gpio_platform_data *pdata;
    struct i2c_algo_bit_data *bit_data;
    struct i2c_adapter *adap;
    int ret;

    priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
    if (!priv)
        return -ENOMEM;
    adap = &priv->adap;
    bit_data = &priv->bit_data;
    pdata = &priv->pdata;

    if (pdev->dev.of_node) {
        ret = of_i2c_gpio_probe(pdev->dev.of_node, pdata);
        if (ret)
            return ret;
    } else {
        if (!pdev->dev.platform_data)
            return -ENXIO;
        memcpy(pdata, pdev->dev.platform_data, sizeof(*pdata));
    }

    ret = gpio_request(pdata->sda_pin, "sda");
    if (ret)
        goto err_request_sda;
    ret = gpio_request(pdata->scl_pin, "scl");
    if (ret)
        goto err_request_scl;

    if (pdata->sda_is_open_drain) {
        gpio_direction_output(pdata->sda_pin, 1);
        bit_data->setsda = i2c_gpio_setsda_val;
    } else {
        gpio_direction_input(pdata->sda_pin);
        bit_data->setsda = i2c_gpio_setsda_dir;
    }

    if (pdata->scl_is_open_drain || pdata->scl_is_output_only) {
        gpio_direction_output(pdata->scl_pin, 1);
        bit_data->setscl = i2c_gpio_setscl_val;
    } else {
        gpio_direction_input(pdata->scl_pin);
        bit_data->setscl = i2c_gpio_setscl_dir;
    }

    if (!pdata->scl_is_output_only)
        bit_data->getscl = i2c_gpio_getscl;
    bit_data->getsda = i2c_gpio_getsda;

    if (pdata->udelay)
        bit_data->udelay = pdata->udelay;
    else if (pdata->scl_is_output_only)
        bit_data->udelay = 50;          /* 10 kHz */
    else
        bit_data->udelay = 5;           /* 100 kHz */

    if (pdata->timeout)
        bit_data->timeout = pdata->timeout;
    else
        bit_data->timeout = HZ / 10;        /* 100 ms */

    bit_data->data = pdata;

    adap->owner = THIS_MODULE;
    snprintf(adap->name, sizeof(adap->name), "i2c-gpio%d", pdev->id);
    adap->algo_data = bit_data;
    adap->class = I2C_CLASS_HWMON | I2C_CLASS_SPD;
    adap->dev.parent = &pdev->dev;
    adap->dev.of_node = pdev->dev.of_node;

    adap->nr = pdev->id;
    ret = i2c_bit_add_numbered_bus(adap);
    if (ret)
        goto err_add_bus;

    of_i2c_register_devices(adap);

    platform_set_drvdata(pdev, priv);

    dev_info(&pdev->dev, "using pins %u (SDA) and %u (SCL%s)\n",
         pdata->sda_pin, pdata->scl_pin,
         pdata->scl_is_output_only
         ? ", no clock stretching" : "");

    return 0;

err_add_bus:
    gpio_free(pdata->scl_pin);
err_request_scl:
    gpio_free(pdata->sda_pin);
err_request_sda:
    return ret;
}

static int __devexit i2c_gpio_remove(struct platform_device *pdev)
{
    struct i2c_gpio_private_data *priv;
    struct i2c_gpio_platform_data *pdata;
    struct i2c_adapter *adap;

    priv = platform_get_drvdata(pdev);
    adap = &priv->adap;
    pdata = &priv->pdata;

    i2c_del_adapter(adap);
    gpio_free(pdata->scl_pin);
    gpio_free(pdata->sda_pin);

    return 0;
}

#if defined(CONFIG_OF)
static const struct of_device_id i2c_gpio_dt_ids[] = {
    { .compatible = "i2c-gpio", },
    { /* sentinel */ }
};

MODULE_DEVICE_TABLE(of, i2c_gpio_dt_ids);
#endif

static struct platform_driver i2c_gpio_driver = {
    .driver     = {
        .name   = "i2c-gpio",
        .owner  = THIS_MODULE,
        .of_match_table = of_match_ptr(i2c_gpio_dt_ids),
    },
    .probe      = i2c_gpio_probe,
    .remove     = __devexit_p(i2c_gpio_remove),
};

static int __init i2c_gpio_init(void)
{
    int ret;

    ret = platform_driver_register(&i2c_gpio_driver);
    if (ret)
        printk(KERN_ERR "i2c-gpio: probe failed: %d\n", ret);

    return ret;
}
subsys_initcall(i2c_gpio_init);

static void __exit i2c_gpio_exit(void)
{
    platform_driver_unregister(&i2c_gpio_driver);
}
module_exit(i2c_gpio_exit);

MODULE_AUTHOR("Haavard Skinnemoen (Atmel)");
MODULE_DESCRIPTION("Platform-independent bitbanging I2C driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:i2c-gpio");