Messages in this thread | | | Date | Sat, 10 Mar 2007 21:15:50 +0100 | From | Jean Delvare <> | Subject | Re: [PATCH v2] Bitbanging i2c bus driver using the GPIO API |
| |
Hi Haavard,
On Sat, 10 Mar 2007 14:13:28 +0100, Haavard Skinnemoen wrote: > 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.
I like the idea very much. Would this let us get rid of i2c-ixp2000? i2c-ixp4xx? scx200_i2c? Other drivers?
> 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
I'm told we're in year 2007 ;)
> + * > + * 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); > +}
What value will you get if the SDA pin is open-drain and currently in output mode? Are such GPIO pins actually able to detect that the pin is low while they are not themselves driving it low?
> + > +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 */
Actually, no, i2c-algo-bit has a 1/3-2/3 duty cycle, so a complete cycle is 3 times the udelay value. So udelay=5 gives you 66 kHz. If someone wants to fix that...
Also, I wouldn't recommend such a low value when SCL cannot be sensed, if a slave stretches the line even very briefly, you won't notice and havoc will ensue. udelay=50 sounds more reasonable for such half-baked busses.
> + 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);
Add KERN_ERR or similar.
> + > + 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 */
Would you mind also adding yourself to MAINTAINERS for this driver? I would appreciate it.
Thanks, -- Jean Delvare - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |