Documentation/i2c/muxes/i2c-mux-gpio.rst
Author: Peter Korsgaard [email protected]
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.
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.
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.