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- .. SPDX-License-Identifier: GPL-2.0-only
- GPIO Testing Driver
- ===================
- .. note::
- This module has been obsoleted by the more flexible gpio-sim.rst.
- New developments should use that API and existing developments are
- encouraged to migrate as soon as possible.
- This module will continue to be maintained but no new features will be
- added.
- 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 (non-negative integer)
- and the first number after the last of this chip. If the base GPIO
- is -1, the gpiolib will assign it automatically. while the following
- parameter is the number of lines exposed by the chip.
- Example: gpio_mockup_ranges=-1,8,-1,16,405,409
- 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_mockup_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).
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