[PATCH v2] Bitbanging i2c bus driver using the GPIO API

[Haavard Skinnemoen <hskinnemoen@atmel.com>]

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.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
---
This patch is different from the first patch in the following ways:
  * Handles pins set up as open drain (aka multidrive) by toggling
    the output value instead of the direction
  * Handles output-only SCL pins the same way, and also does not
    install a getscl() callback for such pins
  * Does not add anything to include/linux/i2c-ids.h
  * Sets the output value explicitly after changing the direction to
    output.
  * Plugs a memory leak in remove() -- algo_data wasn't freed.
  * Prints out the pin IDs in decimal, with an extra note when clock
    stretching isn't supported

This version has been compile-tested only. I'll give it a spin when I
get back to work on monday.

Dave, does this address your concerns?

Haavard   

 drivers/i2c/busses/Kconfig    |    8 ++
 drivers/i2c/busses/Makefile   |    1 +
 drivers/i2c/busses/i2c-gpio.c |  211 +++++++++++++++++++++++++++++++++++++++++
 include/linux/i2c-gpio.h      |   30 ++++++
 4 files changed, 250 insertions(+), 0 deletions(-)

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index fb19dbb..52f79d1 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -102,6 +102,14 @@ 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 driver"
+	depends on I2C && 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 I2C && PCI && PPC_CHRP && EXPERIMENTAL
diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
index 290b540..68f2b05 100644
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -11,6 +11,7 @@ obj-$(CONFIG_I2C_AMD8111)	+= i2c-amd8111.o
 obj-$(CONFIG_I2C_AT91)		+= i2c-at91.o
 obj-$(CONFIG_I2C_AU1550)	+= i2c-au1550.o
 obj-$(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
diff --git a/drivers/i2c/busses/i2c-gpio.c b/drivers/i2c/busses/i2c-gpio.c
new file mode 100644
index 0000000..423db0a
--- /dev/null
+++ b/drivers/i2c/busses/i2c-gpio.c
@@ -0,0 +1,211 @@
+/*
+ * Bitbanging i2c bus driver using the GPIO API
+ *
+ * Copyright (C) 2006 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);
+		gpio_set_value(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);
+		gpio_set_value(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);
+		gpio_set_value(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);
+		gpio_set_value(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,
+	bit_data->udelay	= 5,			/* 100 kHz */
+	bit_data->timeout	= HZ / 10,		/* 100 ms */
+	bit_data->data		= pdata;
+
+	adap->owner = THIS_MODULE;
+	snprintf(adap->name, I2C_NAME_SIZE, "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("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");
diff --git a/include/linux/i2c-gpio.h b/include/linux/i2c-gpio.h
new file mode 100644
index 0000000..1e8fa29
--- /dev/null
+++ b/include/linux/i2c-gpio.h
@@ -0,0 +1,30 @@
+/*
+ * 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
+ * @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.
+ * @scl_is_open_drain: SCL is set up as open drain.
+ * @scl_is_output_only: SCL output drivers cannot be turned off.
+ */
+struct i2c_gpio_platform_data {
+	unsigned int sda_pin;
+	unsigned int scl_pin;
+	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 */
-- 
1.4.4.4