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i2c-gpio.c

/*
 * 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/platform_device.h>

#include <asm/gpio.h>

/* 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 __init i2c_gpio_probe(struct platform_device *pdev)
{
      struct i2c_gpio_platform_data *pdata;
      struct i2c_algo_bit_data *bit_data;
      struct i2c_adapter *adap;
      int ret;

      pdata = pdev->dev.platform_data;
      if (!pdata)
            return -ENXIO;

      ret = -ENOMEM;
      adap = kzalloc(sizeof(struct i2c_adapter), GFP_KERNEL);
      if (!adap)
            goto err_alloc_adap;
      bit_data = kzalloc(sizeof(struct i2c_algo_bit_data), GFP_KERNEL);
      if (!bit_data)
            goto err_alloc_bit_data;

      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;
      adap->dev.parent = &pdev->dev;

      /*
       * If "dev->id" is negative we consider it as zero.
       * The reason to do so is to avoid sysfs names that only make
       * sense when there are multiple adapters.
       */
      adap->nr = (pdev->id != -1) ? pdev->id : 0;
      ret = i2c_bit_add_numbered_bus(adap);
      if (ret)
            goto err_add_bus;

      platform_set_drvdata(pdev, adap);

      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:
      kfree(bit_data);
err_alloc_bit_data:
      kfree(adap);
err_alloc_adap:
      return ret;
}

static int __exit i2c_gpio_remove(struct platform_device *pdev)
{
      struct i2c_gpio_platform_data *pdata;
      struct i2c_adapter *adap;

      adap = platform_get_drvdata(pdev);
      pdata = pdev->dev.platform_data;

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

      return 0;
}

static struct platform_driver i2c_gpio_driver = {
      .driver           = {
            .name = "i2c-gpio",
            .owner      = THIS_MODULE,
      },
      .remove           = __exit_p(i2c_gpio_remove),
};

static int __init i2c_gpio_init(void)
{
      int ret;

      ret = platform_driver_probe(&i2c_gpio_driver, i2c_gpio_probe);
      if (ret)
            printk(KERN_ERR "i2c-gpio: probe failed: %d\n", ret);

      return ret;
}
module_init(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 <hskinnemoen@atmel.com>");
MODULE_DESCRIPTION("Platform-independent bitbanging I2C driver");
MODULE_LICENSE("GPL");

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