[PATCH v3] Bitbanging i2c bus driver using the GPIO API

Haavard Skinnemoen
2007-04-14T12:57:19Z

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 changing the direction of the SDA
and SCL lines on the fly.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
---
Sorry for the long delay. I didn't want to send out a patch just
before taking off for two weeks. This patch contains the following
changes compared to v2:

o Make udelay and timeout parameterizable and fix comment
o Default to a very low SCL frequency (6.6 kHz) if clock stretching
isn't supported
o Document that GPIO hardware must report actual state of sda and
scl pins in open drain mode.
o Add myself to MAINTAINERS
o Add KERN_ERR to "probe failed" message
o Use new gpio_direction_output() API

MAINTAINERS | 5 +
drivers/i2c/busses/Kconfig | 8 ++
drivers/i2c/busses/Makefile | 1 +
drivers/i2c/busses/i2c-gpio.c | 213 +++++++++++++++++++++++++++++++++++++++++
include/linux/i2c-gpio.h | 38 +++++++
5 files changed, 265 insertions(+), 0 deletions(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index ef84419..fdecda4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1429,6 +1429,11 @@ 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
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..895d150
--- /dev/null
+++ b/drivers/i2c/busses/i2c-gpio.c
@@ -0,0 +1,213 @@
+/*
+ * 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
+ bit_data->udelay = 50; /* 66 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, 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(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");
diff --git a/include/linux/i2c-gpio.h b/include/linux/i2c-gpio.h
new file mode 100644
index 0000000..7812407
--- /dev/null
+++ b/include/linux/i2c-gpio.h
@@ -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 (333 / 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 */
--
1.4.4.4