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Diffstat (limited to 'Documentation/i2c/muxes/i2c-mux-gpio.rst')
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diff --git a/Documentation/i2c/muxes/i2c-mux-gpio.rst b/Documentation/i2c/muxes/i2c-mux-gpio.rst new file mode 100644 index 000000000000..7d27444035c3 --- /dev/null +++ b/Documentation/i2c/muxes/i2c-mux-gpio.rst @@ -0,0 +1,85 @@ +========================== +Kernel driver i2c-mux-gpio +========================== + +Author: Peter Korsgaard <peter.korsgaard@barco.com> + +Description +----------- + +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. + +Usage +----- + +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. + +Device Registration +------------------- + +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. |