Documentation/admin-guide/gpio/gpio-sim.rst

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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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.. SPDX-License-Identifier: GPL-2.0-or-later

Configfs GPIO Simulator
=======================

The configfs GPIO Simulator (gpio-sim) 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 sysfs attributes.

Creating simulated chips
------------------------

The gpio-sim module registers a configfs subsystem called ``'gpio-sim'``. For
details of the configfs filesystem, please refer to the configfs documentation.

The user can create a hierarchy of configfs groups and items as well as modify
values of exposed attributes. Once the chip is instantiated, this hierarchy
will be translated to appropriate device properties. The general structure is:

**Group:** ``/config/gpio-sim``

This is the top directory of the gpio-sim configfs tree.

**Group:** ``/config/gpio-sim/gpio-device``

**Attribute:** ``/config/gpio-sim/gpio-device/dev_name``

**Attribute:** ``/config/gpio-sim/gpio-device/live``

This is a directory representing a GPIO platform device. The ``'dev_name'``
attribute is read-only and allows the user-space to read the platform device
name (e.g. ``'gpio-sim.0'``). The ``'live'`` attribute allows to trigger the
actual creation of the device once it's fully configured. The accepted values
are: ``'1'`` to enable the simulated device and ``'0'`` to disable and tear
it down.

**Group:** ``/config/gpio-sim/gpio-device/gpio-bankX``

**Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/chip_name``

**Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/num_lines``

This group represents a bank of GPIOs under the top platform device. The
``'chip_name'`` attribute is read-only and allows the user-space to read the
device name of the bank device. The ``'num_lines'`` attribute allows to specify
the number of lines exposed by this bank.

**Group:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY``

**Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY/name``

**Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY/valid``

This group represents a single line at the offset Y. The ``valid`` attribute
indicates whether the line can be used as GPIO. The ``name`` attribute allows
to set the line name as represented by the 'gpio-line-names' property.

**Item:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY/hog``

**Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY/hog/name``

**Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY/hog/direction``

This item makes the gpio-sim module hog the associated line. The ``'name'``
attribute specifies the in-kernel consumer name to use. The ``'direction'``
attribute specifies the hog direction and must be one of: ``'input'``,
``'output-high'`` and ``'output-low'``.

Inside each bank directory, there's a set of attributes that can be used to

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Implementation Notes