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i2c: Bitbanging I2C bus driver using the GPIO API 

This is a very simple bitbanging I2C bus driver utilizing the new
arch-neutral GPIO API. Useful for chips that don't have a built-in
I2C controller, additional I2C busses, or testing purposes.

To use, include something similar to the following in the
board-specific setup code:

  #include <linux/i2c-gpio.h>

  static struct i2c_gpio_platform_data i2c_gpio_data = {
	.sda_pin	= GPIO_PIN_FOO,
	.scl_pin	= GPIO_PIN_BAR,
  };
  static struct platform_device i2c_gpio_device = {
	.name		= "i2c-gpio",
	.id		= 0,
	.dev		= {
		.platform_data	= &i2c_gpio_data,
	},
  };

Register this platform_device, set up the I2C pins as GPIO if
required and you're ready to go. This will use default values for
udelay and timeout, and will work with GPIO hardware that does not
support open drain mode, but allows sensing of the SDA and SCL lines
even when they are being driven.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
This commit is contained in:
Haavard Skinnemoen 2007-05-01 23:26:34 +02:00 committed by Jean Delvare
parent 16538e6b32
commit 1c23af90dc
5 changed files with 267 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
MAINTAINERS
View File

@ -1466,6 +1466,11 @@ L: linux-scsi@vger.kernel.org
W: http://www.icp-vortex.com/
S: Supported
GENERIC GPIO I2C DRIVER
P: Haavard Skinnemoen
M: hskinnemoen@atmel.com
S: Supported
GENERIC HDLC DRIVER, N2, C101, PCI200SYN and WANXL DRIVERS
P: Krzysztof Halasa
M: khc@pm.waw.pl

8
drivers/i2c/busses/Kconfig
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@ -117,6 +117,14 @@ config I2C_ELEKTOR
This support is also available as a module. If so, the module
will be called i2c-elektor.
config I2C_GPIO
tristate "GPIO-based bitbanging I2C"
depends on GENERIC_GPIO
select I2C_ALGOBIT
help
This is a very simple bitbanging I2C driver utilizing the
arch-neutral GPIO API to control the SCL and SDA lines.
config I2C_HYDRA
tristate "CHRP Apple Hydra Mac I/O I2C interface"
depends on PCI && PPC_CHRP && EXPERIMENTAL

1
drivers/i2c/busses/Makefile
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@ -12,6 +12,7 @@ obj-$(CONFIG_I2C_AT91) += i2c-at91.o
obj-$(CONFIG_I2C_AU1550) += i2c-au1550.o
obj-$(CONFIG_I2C_BLACKFIN_TWI) += i2c-bfin-twi.o
obj-$(CONFIG_I2C_ELEKTOR) += i2c-elektor.o
obj-$(CONFIG_I2C_GPIO) += i2c-gpio.o
obj-$(CONFIG_I2C_HYDRA) += i2c-hydra.o
obj-$(CONFIG_I2C_I801) += i2c-i801.o
obj-$(CONFIG_I2C_I810) += i2c-i810.o

215
drivers/i2c/busses/i2c-gpio.c Normal file
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@ -0,0 +1,215 @@
/*
* 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);
}
int i2c_gpio_getsda(void *data)
{
struct i2c_gpio_platform_data *pdata = data;
return gpio_get_value(pdata->sda_pin);
}
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->dev.parent = &pdev->dev;
ret = i2c_bit_add_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");

38
include/linux/i2c-gpio.h Normal file
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@ -0,0 +1,38 @@
/*
* i2c-gpio interface to platform code
*
* 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.
*/
#ifndef _LINUX_I2C_GPIO_H
#define _LINUX_I2C_GPIO_H
/**
* struct i2c_gpio_platform_data - Platform-dependent data for i2c-gpio
* @sda_pin: GPIO pin ID to use for SDA
* @scl_pin: GPIO pin ID to use for SCL
* @udelay: signal toggle delay. SCL frequency is (500 / udelay) kHz
* @timeout: clock stretching timeout in jiffies. If the slave keeps
* SCL low for longer than this, the transfer will time out.
* @sda_is_open_drain: SDA is configured as open drain, i.e. the pin
* isn't actively driven high when setting the output value high.
* gpio_get_value() must return the actual pin state even if the
* pin is configured as an output.
* @scl_is_open_drain: SCL is set up as open drain. Same requirements
* as for sda_is_open_drain apply.
* @scl_is_output_only: SCL output drivers cannot be turned off.
*/
struct i2c_gpio_platform_data {
unsigned int sda_pin;
unsigned int scl_pin;
int udelay;
int timeout;
unsigned int sda_is_open_drain:1;
unsigned int scl_is_open_drain:1;
unsigned int scl_is_output_only:1;
};
#endif /* _LINUX_I2C_GPIO_H */