linux/drivers/i2c/busses/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/slab.h>
#include <linux/platform_device.h>
#include <linux/gpio/consumer.h>
#include <linux/of.h>

struct i2c_gpio_private_data {
	struct gpio_desc *sda;
	struct gpio_desc *scl;
	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_private_data *priv = data;

	/*
	 * This is a way of saying "do not drive
	 * me actively high" which means emulating open drain.
	 * The right way to do this is for gpiolib to
	 * handle this, by the function below.
	 */
	if (state)
		gpiod_direction_input(priv->sda);
	else
		gpiod_direction_output(priv->sda, 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_private_data *priv = data;

	gpiod_set_value(priv->sda, state);
}

/* Toggle SCL by changing the direction of the pin. */
static void i2c_gpio_setscl_dir(void *data, int state)
{
	struct i2c_gpio_private_data *priv = data;

	if (state)
		gpiod_direction_input(priv->scl);
	else
		gpiod_direction_output(priv->scl, 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_private_data *priv = data;

	gpiod_set_value(priv->scl, state);
}

static int i2c_gpio_getsda(void *data)
{
	struct i2c_gpio_private_data *priv = data;

	return gpiod_get_value(priv->sda);
}

static int i2c_gpio_getscl(void *data)
{
	struct i2c_gpio_private_data *priv = data;

	return gpiod_get_value(priv->scl);
}

static void of_i2c_gpio_get_props(struct device_node *np,
				  struct i2c_gpio_platform_data *pdata)
{
	u32 reg;

	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");
}

static int 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;

	/* First get the GPIO pins; if it fails, we'll defer the probe. */
	priv->sda = devm_gpiod_get_index(&pdev->dev, NULL, 0, GPIOD_OUT_HIGH);
	if (IS_ERR(priv->sda)) {
		ret = PTR_ERR(priv->sda);
		/* FIXME: hack in the old code, is this really necessary? */
		if (ret == -EINVAL)
			ret = -EPROBE_DEFER;
		return ret;
	}
	priv->scl = devm_gpiod_get_index(&pdev->dev, NULL, 1, GPIOD_OUT_LOW);
	if (IS_ERR(priv->scl)) {
		ret = PTR_ERR(priv->scl);
		/* FIXME: hack in the old code, is this really necessary? */
		if (ret == -EINVAL)
			ret = -EPROBE_DEFER;
		return ret;
	}

	adap = &priv->adap;
	bit_data = &priv->bit_data;
	pdata = &priv->pdata;

	if (pdev->dev.of_node) {
		of_i2c_gpio_get_props(pdev->dev.of_node, pdata);
	} else {
		/*
		 * If all platform data settings are zero it is OK
		 * to not provide any platform data from the board.
		 */
		if (dev_get_platdata(&pdev->dev))
			memcpy(pdata, dev_get_platdata(&pdev->dev),
			       sizeof(*pdata));
	}

	/*
	 * FIXME: this is a hack emulating the open drain emulation
	 * that gpiolib can already do for us. Make all clients properly
	 * flag their lines as open drain and get rid of this property
	 * and the special callback.
	 */
	if (pdata->sda_is_open_drain) {
		gpiod_direction_output(priv->sda, 1);
		bit_data->setsda = i2c_gpio_setsda_val;
	} else {
		gpiod_direction_input(priv->sda);
		bit_data->setsda = i2c_gpio_setsda_dir;
	}

	if (pdata->scl_is_open_drain || pdata->scl_is_output_only) {
		gpiod_direction_output(priv->scl, 1);
		bit_data->setscl = i2c_gpio_setscl_val;
	} else {
		gpiod_direction_input(priv->scl);
		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 = priv;

	adap->owner = THIS_MODULE;
	if (pdev->dev.of_node)
		strlcpy(adap->name, dev_name(&pdev->dev), sizeof(adap->name));
	else
		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)
		return ret;

	platform_set_drvdata(pdev, priv);

	/*
	 * FIXME: using global GPIO numbers is not helpful. If/when we
	 * get accessors to get the actual name of the GPIO line,
	 * from the descriptor, then provide that instead.
	 */
	dev_info(&pdev->dev, "using lines %u (SDA) and %u (SCL%s)\n",
		 desc_to_gpio(priv->sda), desc_to_gpio(priv->scl),
		 pdata->scl_is_output_only
		 ? ", no clock stretching" : "");

	return 0;
}

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

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

	i2c_del_adapter(adap);

	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",
		.of_match_table	= of_match_ptr(i2c_gpio_dt_ids),
	},
	.probe		= i2c_gpio_probe,
	.remove		= 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");