51 lines
1.9 KiB
ReStructuredText
51 lines
1.9 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-only
|
|
|
|
GPIO Testing Driver
|
|
===================
|
|
|
|
The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO
|
|
chips for testing purposes. The lines exposed by these chips can be accessed
|
|
using the standard GPIO character device interface as well as manipulated
|
|
using the dedicated debugfs directory structure.
|
|
|
|
Creating simulated chips using module params
|
|
--------------------------------------------
|
|
|
|
When loading the gpio-mockup driver a number of parameters can be passed to the
|
|
module.
|
|
|
|
gpio_mockup_ranges
|
|
|
|
This parameter takes an argument in the form of an array of integer
|
|
pairs. Each pair defines the base GPIO number (if any) and the number
|
|
of lines exposed by the chip. If the base GPIO is -1, the gpiolib
|
|
will assign it automatically.
|
|
|
|
Example: gpio_mockup_ranges=-1,8,-1,16,405,4
|
|
|
|
The line above creates three chips. The first one will expose 8 lines,
|
|
the second 16 and the third 4. The base GPIO for the third chip is set
|
|
to 405 while for two first chips it will be assigned automatically.
|
|
|
|
gpio_named_lines
|
|
|
|
This parameter doesn't take any arguments. It lets the driver know that
|
|
GPIO lines exposed by it should be named.
|
|
|
|
The name format is: gpio-mockup-X-Y where X is mockup chip's ID
|
|
and Y is the line offset.
|
|
|
|
Manipulating simulated lines
|
|
----------------------------
|
|
|
|
Each mockup chip creates its own subdirectory in /sys/kernel/debug/gpio-mockup/.
|
|
The directory is named after the chip's label. A symlink is also created, named
|
|
after the chip's name, which points to the label directory.
|
|
|
|
Inside each subdirectory, there's a separate attribute for each GPIO line. The
|
|
name of the attribute represents the line's offset in the chip.
|
|
|
|
Reading from a line attribute returns the current value. Writing to it (0 or 1)
|
|
changes the configuration of the simulated pull-up/pull-down resistor
|
|
(1 - pull-up, 0 - pull-down).
|