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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /Documentation/i2c/muxes
parentInitial commit. (diff)
downloadlinux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz
linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip
Adding upstream version 6.1.76.upstream/6.1.76upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+==========================
+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.