1 .. SPDX-License-Identifier: GPL-2.0-only
8 This module has been obsoleted by the more flexible gpio-sim.rst.
9 New developments should use that API and existing developments are
10 encouraged to migrate as soon as possible.
11 This module will continue to be maintained but no new features will be
14 The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO
15 chips for testing purposes. The lines exposed by these chips can be accessed
16 using the standard GPIO character device interface as well as manipulated
17 using the dedicated debugfs directory structure.
19 Creating simulated chips using module params
20 --------------------------------------------
22 When loading the gpio-mockup driver a number of parameters can be passed to the
27 This parameter takes an argument in the form of an array of integer
28 pairs. Each pair defines the base GPIO number (non-negative integer)
29 and the first number after the last of this chip. If the base GPIO
30 is -1, the gpiolib will assign it automatically. while the following
31 parameter is the number of lines exposed by the chip.
33 Example: gpio_mockup_ranges=-1,8,-1,16,405,409
35 The line above creates three chips. The first one will expose 8 lines,
36 the second 16 and the third 4. The base GPIO for the third chip is set
37 to 405 while for two first chips it will be assigned automatically.
39 gpio_mockup_named_lines
41 This parameter doesn't take any arguments. It lets the driver know that
42 GPIO lines exposed by it should be named.
44 The name format is: gpio-mockup-X-Y where X is mockup chip's ID
45 and Y is the line offset.
47 Manipulating simulated lines
48 ----------------------------
50 Each mockup chip creates its own subdirectory in /sys/kernel/debug/gpio-mockup/.
51 The directory is named after the chip's label. A symlink is also created, named
52 after the chip's name, which points to the label directory.
54 Inside each subdirectory, there's a separate attribute for each GPIO line. The
55 name of the attribute represents the line's offset in the chip.
57 Reading from a line attribute returns the current value. Writing to it (0 or 1)
58 changes the configuration of the simulated pull-up/pull-down resistor
59 (1 - pull-up, 0 - pull-down).