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i2c-mux-gpio_driver.txt
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--------------------------------------------------------------------------------------
from kernel/Documentation/i2c/muxes/i2c-mux-gpio/
--------------------------------------------------------------------------------------
Kernel driver i2c-mux-gpio
Author: Peter Korsgaard <peter.korsgaard@barco.com>
Description
-----------
i2c-mux-gpio is an i2c mux driver providing access to I2C bus segments
from a master I2C bus and a hardware MUX controlled through GPIO pins.
E.G.:
---------- ---------- Bus segment 1 - - - - -
| | SCL/SDA | |-------------- | |
| |------------| |
| | | | Bus segment 2 | |
| Linux | GPIO 1..N | MUX |--------------- Devices
| |------------| | | |
| | | | Bus segment M
| | | |---------------| |
---------- ---------- - - - - -
SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M
according to the settings of the GPIO pins 1..N.
Usage
-----
i2c-mux-gpio uses the platform bus, so you need to provide a struct
platform_device with the platform_data pointing to a struct
i2c_mux_gpio_platform_data with the I2C adapter number of the master
bus, the number of bus segments to create and the GPIO pins used
to control it. See include/linux/platform_data/i2c-mux-gpio.h for details.
E.G. something like this for a MUX providing 4 bus segments
controlled through 3 GPIO pins:
#include <linux/platform_data/i2c-mux-gpio.h>
#include <linux/platform_device.h>
static const unsigned myboard_gpiomux_gpios[] = {
AT91_PIN_PC26, AT91_PIN_PC25, AT91_PIN_PC24
};
static const unsigned myboard_gpiomux_values[] = {
0, 1, 2, 3
};
static struct i2c_mux_gpio_platform_data myboard_i2cmux_data = {
.parent = 1,
.base_nr = 2, /* optional */
.values = myboard_gpiomux_values,
.n_values = ARRAY_SIZE(myboard_gpiomux_values),
.gpios = myboard_gpiomux_gpios,
.n_gpios = ARRAY_SIZE(myboard_gpiomux_gpios),
.idle = 4, /* optional */
};
static struct platform_device myboard_i2cmux = {
.name = "i2c-mux-gpio",
.id = 0,
.dev = {
.platform_data = &myboard_i2cmux_data,
},
};
If you don't know the absolute GPIO pin numbers at registration time,
you can instead provide a chip name (.chip_name) and relative GPIO pin
numbers, and the i2c-mux-gpio driver will do the work for you,
including deferred probing if the GPIO chip isn't immediately
available.
Device Registration
-------------------
When registering your i2c-mux-gpio device, you should pass the number
of any GPIO pin it uses as the device ID. This guarantees that every
instance has a different ID.
Alternatively, if you don't need a stable device name, you can simply
pass PLATFORM_DEVID_AUTO as the device ID, and the platform core will
assign a dynamic ID to your device. If you do not know the absolute
GPIO pin numbers at registration time, this is even the only option.