1 ==========================
2 Kernel driver i2c-mux-gpio
3 ==========================
4
5 Author: Peter Korsgaard <peter.korsgaard@barco.com>
6
7 Description
8 -----------
9
10 i2c-mux-gpio is an i2c mux driver providing access to I2C bus segments
11 from a master I2C bus and a hardware MUX controlled through GPIO pins.
12
13 E.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
25 SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M
26 according to the settings of the GPIO pins 1..N.
27
28 Usage
29 -----
30
31 i2c-mux-gpio uses the platform bus, so you need to provide a struct
32 platform_device with the platform_data pointing to a struct
33 i2c_mux_gpio_platform_data with the I2C adapter number of the master
34 bus, the number of bus segments to create and the GPIO pins used
35 to control it. See include/linux/platform_data/i2c-mux-gpio.h for details.
36
37 E.G. something like this for a MUX providing 4 bus segments
38 controlled 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
69 If you don't know the absolute GPIO pin numbers at registration time,
70 you can instead provide a chip name (.chip_name) and relative GPIO pin
71 numbers, and the i2c-mux-gpio driver will do the work for you,
72 including deferred probing if the GPIO chip isn't immediately
73 available.
74
75 Device Registration
76 -------------------
77
78 When registering your i2c-mux-gpio device, you should pass the number
79 of any GPIO pin it uses as the device ID. This guarantees that every
80 instance has a different ID.
81
82 Alternatively, if you don't need a stable device name, you can simply
83 pass PLATFORM_DEVID_AUTO as the device ID, and the platform core will
84 assign a dynamic ID to your device. If you do not know the absolute
85 GPIO pin numbers at registration time, this is even the only option.
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