84 lines
2.7 KiB
Text
84 lines
2.7 KiB
Text
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Kernel driver i2c-gpio-mux
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Author: Peter Korsgaard <peter.korsgaard@barco.com>
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Description
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-----------
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i2c-gpio-mux is an i2c mux driver providing access to I2C bus segments
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from a master I2C bus and a hardware MUX controlled through GPIO pins.
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E.G.:
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---------- ---------- Bus segment 1 - - - - -
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| | SCL/SDA | |-------------- | |
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| |------------| |
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| | | | Bus segment 2 | |
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| Linux | GPIO 1..N | MUX |--------------- Devices
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| |------------| | | |
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| | | | Bus segment M
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| | | |---------------| |
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---------- ---------- - - - - -
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SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M
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according to the settings of the GPIO pins 1..N.
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Usage
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-----
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i2c-gpio-mux uses the platform bus, so you need to provide a struct
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platform_device with the platform_data pointing to a struct
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gpio_i2cmux_platform_data with the I2C adapter number of the master
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bus, the number of bus segments to create and the GPIO pins used
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to control it. See include/linux/i2c-gpio-mux.h for details.
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E.G. something like this for a MUX providing 4 bus segments
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controlled through 3 GPIO pins:
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#include <linux/i2c-gpio-mux.h>
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#include <linux/platform_device.h>
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static const unsigned myboard_gpiomux_gpios[] = {
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AT91_PIN_PC26, AT91_PIN_PC25, AT91_PIN_PC24
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};
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static const unsigned myboard_gpiomux_values[] = {
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0, 1, 2, 3
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};
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static struct gpio_i2cmux_platform_data myboard_i2cmux_data = {
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.parent = 1,
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.base_nr = 2, /* optional */
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.values = myboard_gpiomux_values,
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.n_values = ARRAY_SIZE(myboard_gpiomux_values),
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.gpios = myboard_gpiomux_gpios,
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.n_gpios = ARRAY_SIZE(myboard_gpiomux_gpios),
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.idle = 4, /* optional */
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};
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static struct platform_device myboard_i2cmux = {
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.name = "i2c-gpio-mux",
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.id = 0,
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.dev = {
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.platform_data = &myboard_i2cmux_data,
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},
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};
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If you don't know the absolute GPIO pin numbers at registration time,
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you can instead provide a chip name (.chip_name) and relative GPIO pin
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numbers, and the i2c-gpio-mux driver will do the work for you,
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including deferred probing if the GPIO chip isn't immediately
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available.
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Device Registration
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-------------------
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When registering your i2c-gpio-mux device, you should pass the number
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of any GPIO pin it uses as the device ID. This guarantees that every
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instance has a different ID.
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Alternatively, if you don't need a stable device name, you can simply
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pass PLATFORM_DEVID_AUTO as the device ID, and the platform core will
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assign a dynamic ID to your device. If you do not know the absolute
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GPIO pin numbers at registration time, this is even the only option.
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