0001 ==========================
0002 Kernel driver i2c-mux-gpio
0003 ==========================
0004
0005 Author: Peter Korsgaard <peter.korsgaard@barco.com>
0006
0007 Description
0008 -----------
0009
0010 i2c-mux-gpio is an i2c mux driver providing access to I2C bus segments
0011 from a master I2C bus and a hardware MUX controlled through GPIO pins.
0012
0013 E.G.::
0014
0015 ---------- ---------- Bus segment 1 - - - - -
0016 | | SCL/SDA | |-------------- | |
0017 | |------------| |
0018 | | | | Bus segment 2 | |
0019 | Linux | GPIO 1..N | MUX |--------------- Devices
0020 | |------------| | | |
0021 | | | | Bus segment M
0022 | | | |---------------| |
0023 ---------- ---------- - - - - -
0024
0025 SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M
0026 according to the settings of the GPIO pins 1..N.
0027
0028 Usage
0029 -----
0030
0031 i2c-mux-gpio uses the platform bus, so you need to provide a struct
0032 platform_device with the platform_data pointing to a struct
0033 i2c_mux_gpio_platform_data with the I2C adapter number of the master
0034 bus, the number of bus segments to create and the GPIO pins used
0035 to control it. See include/linux/platform_data/i2c-mux-gpio.h for details.
0036
0037 E.G. something like this for a MUX providing 4 bus segments
0038 controlled through 3 GPIO pins::
0039
0040 #include <linux/platform_data/i2c-mux-gpio.h>
0041 #include <linux/platform_device.h>
0042
0043 static const unsigned myboard_gpiomux_gpios[] = {
0044 AT91_PIN_PC26, AT91_PIN_PC25, AT91_PIN_PC24
0045 };
0046
0047 static const unsigned myboard_gpiomux_values[] = {
0048 0, 1, 2, 3
0049 };
0050
0051 static struct i2c_mux_gpio_platform_data myboard_i2cmux_data = {
0052 .parent = 1,
0053 .base_nr = 2, /* optional */
0054 .values = myboard_gpiomux_values,
0055 .n_values = ARRAY_SIZE(myboard_gpiomux_values),
0056 .gpios = myboard_gpiomux_gpios,
0057 .n_gpios = ARRAY_SIZE(myboard_gpiomux_gpios),
0058 .idle = 4, /* optional */
0059 };
0060
0061 static struct platform_device myboard_i2cmux = {
0062 .name = "i2c-mux-gpio",
0063 .id = 0,
0064 .dev = {
0065 .platform_data = &myboard_i2cmux_data,
0066 },
0067 };
0068
0069 If you don't know the absolute GPIO pin numbers at registration time,
0070 you can instead provide a chip name (.chip_name) and relative GPIO pin
0071 numbers, and the i2c-mux-gpio driver will do the work for you,
0072 including deferred probing if the GPIO chip isn't immediately
0073 available.
0074
0075 Device Registration
0076 -------------------
0077
0078 When registering your i2c-mux-gpio device, you should pass the number
0079 of any GPIO pin it uses as the device ID. This guarantees that every
0080 instance has a different ID.
0081
0082 Alternatively, if you don't need a stable device name, you can simply
0083 pass PLATFORM_DEVID_AUTO as the device ID, and the platform core will
0084 assign a dynamic ID to your device. If you do not know the absolute
0085 GPIO pin numbers at registration time, this is even the only option.
