Documentation/i2c/muxes/i2c-mux-gpio

   1 Kernel driver i2c-gpio-mux
   2
   3 Author: Peter Korsgaard <peter.korsgaard@barco.com>
   4
   5 Description
   6 -----------
   7
   8 i2c-gpio-mux 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-gpio-mux uses the platform bus, so you need to provide a struct
  30 platform_device with the platform_data pointing to a struct
  31 gpio_i2cmux_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-gpio-mux.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-gpio-mux.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 gpio_i2cmux_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-gpio-mux",
  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-gpio-mux 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-gpio-mux 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.