1Kernel driver i2c-mux-gpio
2
3Author: Peter Korsgaard <peter.korsgaard@barco.com>
4
5Description
6-----------
7
8i2c-mux-gpio is an i2c mux driver providing access to I2C bus segments
9from a master I2C bus and a hardware MUX controlled through GPIO pins.
10
11E.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
23SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M
24according to the settings of the GPIO pins 1..N.
25
26Usage
27-----
28
29i2c-mux-gpio uses the platform bus, so you need to provide a struct
30platform_device with the platform_data pointing to a struct
31i2c_mux_gpio_platform_data with the I2C adapter number of the master
32bus, the number of bus segments to create and the GPIO pins used
33to control it. See include/linux/platform_data/i2c-mux-gpio.h for details.
34
35E.G. something like this for a MUX providing 4 bus segments
36controlled through 3 GPIO pins:
37
38#include <linux/platform_data/i2c-mux-gpio.h>
39#include <linux/platform_device.h>
40
41static const unsigned myboard_gpiomux_gpios[] = {
42	AT91_PIN_PC26, AT91_PIN_PC25, AT91_PIN_PC24
43};
44
45static const unsigned myboard_gpiomux_values[] = {
46	0, 1, 2, 3
47};
48
49static struct i2c_mux_gpio_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
59static struct platform_device myboard_i2cmux = {
60	.name		= "i2c-mux-gpio",
61	.id		= 0,
62	.dev		= {
63		.platform_data	= &myboard_i2cmux_data,
64	},
65};
66
67If you don't know the absolute GPIO pin numbers at registration time,
68you can instead provide a chip name (.chip_name) and relative GPIO pin
69numbers, and the i2c-mux-gpio driver will do the work for you,
70including deferred probing if the GPIO chip isn't immediately
71available.
72
73Device Registration
74-------------------
75
76When registering your i2c-mux-gpio device, you should pass the number
77of any GPIO pin it uses as the device ID. This guarantees that every
78instance has a different ID.
79
80Alternatively, if you don't need a stable device name, you can simply
81pass PLATFORM_DEVID_AUTO as the device ID, and the platform core will
82assign a dynamic ID to your device. If you do not know the absolute
83GPIO pin numbers at registration time, this is even the only option.
84