Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 Kernel driver i2c-mux-gpio 2 3 Author: Peter Korsgaard <peter.korsgaard@barco.com> 4 5 Description 6 ----------- 7 8 i2c-mux-gpio is an i2c mux driver providing access to I2C bus segments 9 from a master I2C bus and a hardware MUX controlled through GPIO pins. 10 11 E.G.: 12 13 ---------- ---------- Bus segment 1 - - - - - 14 | | SCL/SDA | |-------------- | | 15 | |------------| | 16 | | | | Bus segment 2 | | 17 | Linux | GPIO 1..N | MUX |--------------- Devices 18 | |------------| | | | 19 | | | | Bus segment M 20 | | | |---------------| | 21 ---------- ---------- - - - - - 22 23 SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M 24 according to the settings of the GPIO pins 1..N. 25 26 Usage 27 ----- 28 29 i2c-mux-gpio uses the platform bus, so you need to provide a struct 30 platform_device with the platform_data pointing to a struct 31 i2c_mux_gpio_platform_data with the I2C adapter number of the master 32 bus, the number of bus segments to create and the GPIO pins used 33 to control it. See include/linux/i2c-mux-gpio.h for details. 34 35 E.G. something like this for a MUX providing 4 bus segments 36 controlled through 3 GPIO pins: 37 38 #include <linux/i2c-mux-gpio.h> 39 #include <linux/platform_device.h> 40 41 static const unsigned myboard_gpiomux_gpios[] = { 42 AT91_PIN_PC26, AT91_PIN_PC25, AT91_PIN_PC24 43 }; 44 45 static const unsigned myboard_gpiomux_values[] = { 46 0, 1, 2, 3 47 }; 48 49 static struct i2c_mux_gpio_platform_data myboard_i2cmux_data = { 50 .parent = 1, 51 .base_nr = 2, /* optional */ 52 .values = myboard_gpiomux_values, 53 .n_values = ARRAY_SIZE(myboard_gpiomux_values), 54 .gpios = myboard_gpiomux_gpios, 55 .n_gpios = ARRAY_SIZE(myboard_gpiomux_gpios), 56 .idle = 4, /* optional */ 57 }; 58 59 static struct platform_device myboard_i2cmux = { 60 .name = "i2c-mux-gpio", 61 .id = 0, 62 .dev = { 63 .platform_data = &myboard_i2cmux_data, 64 }, 65 }; 66 67 If you don't know the absolute GPIO pin numbers at registration time, 68 you can instead provide a chip name (.chip_name) and relative GPIO pin 69 numbers, and the i2c-mux-gpio driver will do the work for you, 70 including deferred probing if the GPIO chip isn't immediately 71 available. 72 73 Device Registration 74 ------------------- 75 76 When registering your i2c-mux-gpio device, you should pass the number 77 of any GPIO pin it uses as the device ID. This guarantees that every 78 instance has a different ID. 79 80 Alternatively, if you don't need a stable device name, you can simply 81 pass PLATFORM_DEVID_AUTO as the device ID, and the platform core will 82 assign a dynamic ID to your device. If you do not know the absolute 83 GPIO pin numbers at registration time, this is even the only option.