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1==========================2Kernel driver i2c-mux-gpio3==========================4 5Author: Peter Korsgaard <peter.korsgaard@barco.com>6 7Description8-----------9 10i2c-mux-gpio is an i2c mux driver providing access to I2C bus segments11from a master I2C bus and a hardware MUX controlled through GPIO pins.12 13E.G.::14 15 ---------- ---------- Bus segment 1 - - - - -16 | | SCL/SDA | |-------------- | |17 | |------------| |18 | | | | Bus segment 2 | |19 | Linux | GPIO 1..N | MUX |--------------- Devices20 | |------------| | | |21 | | | | Bus segment M22 | | | |---------------| |23 ---------- ---------- - - - - -24 25SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M26according to the settings of the GPIO pins 1..N.27 28Usage29-----30 31i2c-mux-gpio uses the platform bus, so you need to provide a struct32platform_device with the platform_data pointing to a struct33i2c_mux_gpio_platform_data with the I2C adapter number of the master34bus, the number of bus segments to create and the GPIO pins used35to control it. See include/linux/platform_data/i2c-mux-gpio.h for details.36 37E.G. something like this for a MUX providing 4 bus segments38controlled through 3 GPIO pins::39 40 #include <linux/platform_data/i2c-mux-gpio.h>41 #include <linux/platform_device.h>42 43 static const unsigned myboard_gpiomux_gpios[] = {44 AT91_PIN_PC26, AT91_PIN_PC25, AT91_PIN_PC2445 };46 47 static const unsigned myboard_gpiomux_values[] = {48 0, 1, 2, 349 };50 51 static struct i2c_mux_gpio_platform_data myboard_i2cmux_data = {52 .parent = 1,53 .base_nr = 2, /* optional */54 .values = myboard_gpiomux_values,55 .n_values = ARRAY_SIZE(myboard_gpiomux_values),56 .gpios = myboard_gpiomux_gpios,57 .n_gpios = ARRAY_SIZE(myboard_gpiomux_gpios),58 .idle = 4, /* optional */59 };60 61 static struct platform_device myboard_i2cmux = {62 .name = "i2c-mux-gpio",63 .id = 0,64 .dev = {65 .platform_data = &myboard_i2cmux_data,66 },67 };68 69If you don't know the absolute GPIO pin numbers at registration time,70you can instead provide a chip name (.chip_name) and relative GPIO pin71numbers, and the i2c-mux-gpio driver will do the work for you,72including deferred probing if the GPIO chip isn't immediately73available.74 75Device Registration76-------------------77 78When registering your i2c-mux-gpio device, you should pass the number79of any GPIO pin it uses as the device ID. This guarantees that every80instance has a different ID.81 82Alternatively, if you don't need a stable device name, you can simply83pass PLATFORM_DEVID_AUTO as the device ID, and the platform core will84assign a dynamic ID to your device. If you do not know the absolute85GPIO pin numbers at registration time, this is even the only option.86