Description¶

i2c-mux-gpio is an i2c mux driver providing access to I2C bus segmentsfrom 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..Maccording to the settings of the GPIO pins 1..N.

Usage¶

i2c-mux-gpio uses the platform bus, so you need to provide a structplatform_device with the platform_data pointing to a structi2c_mux_gpio_platform_data with the I2C adapter number of the masterbus, the number of bus segments to create and the GPIO pins usedto control it. See include/linux/platform_data/i2c-mux-gpio.h for details.

E.G. something like this for a MUX providing 4 bus segmentscontrolled 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 pinnumbers, and the i2c-mux-gpio driver will do the work for you,including deferred probing if the GPIO chip isn’t immediatelyavailable.

Device Registration¶

When registering your i2c-mux-gpio device, you should pass the numberof any GPIO pin it uses as the device ID. This guarantees that everyinstance has a different ID.

Alternatively, if you don’t need a stable device name, you can simplypass PLATFORM_DEVID_AUTO as the device ID, and the platform core willassign a dynamic ID to your device. If you do not know the absoluteGPIO pin numbers at registration time, this is even the only option.