1========================== 2Kernel driver i2c-mux-gpio 3========================== 4 5Author: Peter Korsgaard <peter.korsgaard@barco.com> 6 7Description 8----------- 9 10i2c-mux-gpio is an i2c mux driver providing access to I2C bus segments 11from 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 |--------------- Devices 20 | |------------| | | | 21 | | | | Bus segment M 22 | | | |---------------| | 23 ---------- ---------- - - - - - 24 25SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M 26according to the settings of the GPIO pins 1..N. 27 28Usage 29----- 30 31i2c-mux-gpio uses the platform bus, so you need to provide a struct 32platform_device with the platform_data pointing to a struct 33i2c_mux_gpio_platform_data with the I2C adapter number of the master 34bus, the number of bus segments to create and the GPIO pins used 35to 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 segments 38controlled 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_PC24 45 }; 46 47 static const unsigned myboard_gpiomux_values[] = { 48 0, 1, 2, 3 49 }; 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 pin 71numbers, and the i2c-mux-gpio driver will do the work for you, 72including deferred probing if the GPIO chip isn't immediately 73available. 74 75Device Registration 76------------------- 77 78When registering your i2c-mux-gpio device, you should pass the number 79of any GPIO pin it uses as the device ID. This guarantees that every 80instance has a different ID. 81 82Alternatively, if you don't need a stable device name, you can simply 83pass PLATFORM_DEVID_AUTO as the device ID, and the platform core will 84assign a dynamic ID to your device. If you do not know the absolute 85GPIO pin numbers at registration time, this is even the only option. 86