1.. SPDX-License-Identifier: GPL-2.0-only
2
3GPIO Testing Driver
4===================
5
6The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO
7chips for testing purposes. The lines exposed by these chips can be accessed
8using the standard GPIO character device interface as well as manipulated
9using the dedicated debugfs directory structure.
10
11Creating simulated chips using module params
12--------------------------------------------
13
14When loading the gpio-mockup driver a number of parameters can be passed to the
15module.
16
17    gpio_mockup_ranges
18
19        This parameter takes an argument in the form of an array of integer
20        pairs. Each pair defines the base GPIO number (non-negative integer)
21        and the first number after the last of this chip. If the base GPIO
22        is -1, the gpiolib will assign it automatically. while the following
23        parameter is the number of lines exposed by the chip.
24
25        Example: gpio_mockup_ranges=-1,8,-1,16,405,409
26
27        The line above creates three chips. The first one will expose 8 lines,
28        the second 16 and the third 4. The base GPIO for the third chip is set
29        to 405 while for two first chips it will be assigned automatically.
30
31    gpio_mockup_named_lines
32
33        This parameter doesn't take any arguments. It lets the driver know that
34        GPIO lines exposed by it should be named.
35
36        The name format is: gpio-mockup-X-Y where X is mockup chip's ID
37        and Y is the line offset.
38
39Manipulating simulated lines
40----------------------------
41
42Each mockup chip creates its own subdirectory in /sys/kernel/debug/gpio-mockup/.
43The directory is named after the chip's label. A symlink is also created, named
44after the chip's name, which points to the label directory.
45
46Inside each subdirectory, there's a separate attribute for each GPIO line. The
47name of the attribute represents the line's offset in the chip.
48
49Reading from a line attribute returns the current value. Writing to it (0 or 1)
50changes the configuration of the simulated pull-up/pull-down resistor
51(1 - pull-up, 0 - pull-down).
52