About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / i2c / muxes / i2c-mux-gpio




Custom Search

Based on kernel version 3.13. Page generated on 2014-01-20 22:03 EST.

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.
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.