1==========================
2Kernel driver i2c-mux-gpio
3==========================
4
5Author: Peter Korsgaard <peter.korsgaard@barco.com>
6
7Description
8-----------
9
10i2c-mux-gpio is an i2c mux driver providing access to I2C bus segments
11from a master I2C bus and a hardware MUX controlled through GPIO pins.
12
13E.G.::
14
15  ----------              ----------  Bus segment 1   - - - - -
16 |          | SCL/SDA    |          |-------------- |           |
17 |          |------------|          |
18 |          |            |          | Bus segment 2 |           |
19 |  Linux   | GPIO 1..N  |   MUX    |---------------   Devices
20 |          |------------|          |               |           |
21 |          |            |          | Bus segment M
22 |          |            |          |---------------|           |
23  ----------              ----------                  - - - - -
24
25SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M
26according to the settings of the GPIO pins 1..N.
27
28Usage
29-----
30
31i2c-mux-gpio uses the platform bus, so you need to provide a struct
32platform_device with the platform_data pointing to a struct
33i2c_mux_gpio_platform_data with the I2C adapter number of the master
34bus, the number of bus segments to create and the GPIO pins used
35to control it. See include/linux/platform_data/i2c-mux-gpio.h for details.
36
37E.G. something like this for a MUX providing 4 bus segments
38controlled through 3 GPIO pins::
39
40  #include <linux/platform_data/i2c-mux-gpio.h>
41  #include <linux/platform_device.h>
42
43  static const unsigned myboard_gpiomux_gpios[] = {
44	AT91_PIN_PC26, AT91_PIN_PC25, AT91_PIN_PC24
45  };
46
47  static const unsigned myboard_gpiomux_values[] = {
48	0, 1, 2, 3
49  };
50
51  static struct i2c_mux_gpio_platform_data myboard_i2cmux_data = {
52	.parent		= 1,
53	.base_nr	= 2, /* optional */
54	.values		= myboard_gpiomux_values,
55	.n_values	= ARRAY_SIZE(myboard_gpiomux_values),
56	.gpios		= myboard_gpiomux_gpios,
57	.n_gpios	= ARRAY_SIZE(myboard_gpiomux_gpios),
58	.idle		= 4, /* optional */
59  };
60
61  static struct platform_device myboard_i2cmux = {
62	.name		= "i2c-mux-gpio",
63	.id		= 0,
64	.dev		= {
65		.platform_data	= &myboard_i2cmux_data,
66	},
67  };
68
69If you don't know the absolute GPIO pin numbers at registration time,
70you can instead provide a chip name (.chip_name) and relative GPIO pin
71numbers, and the i2c-mux-gpio driver will do the work for you,
72including deferred probing if the GPIO chip isn't immediately
73available.
74
75Device Registration
76-------------------
77
78When registering your i2c-mux-gpio device, you should pass the number
79of any GPIO pin it uses as the device ID. This guarantees that every
80instance has a different ID.
81
82Alternatively, if you don't need a stable device name, you can simply
83pass PLATFORM_DEVID_AUTO as the device ID, and the platform core will
84assign a dynamic ID to your device. If you do not know the absolute
85GPIO pin numbers at registration time, this is even the only option.
86