.. SPDX-License-Identifier: GPL-2.0
===================================
GPIO Character Device Userspace API
===================================
This is latest version (v2) of the character device API, as defined in
``include/uapi/linux/gpio.h.``
First added in 5.10.
.. note::
Do NOT abuse userspace APIs to control hardware that has proper kernel
drivers. There may already be a driver for your use case, and an existing
kernel driver is sure to provide a superior solution to bitbashing
from userspace.
Read Documentation/driver-api/gpio/drivers-on-gpio.rst to avoid reinventing
kernel wheels in userspace.
Similarly, for multi-function lines there may be other subsystems, such as
Documentation/spi/index.rst, Documentation/i2c/index.rst,
Documentation/driver-api/pwm.rst, Documentation/w1/index.rst etc, that
provide suitable drivers and APIs for your hardware.
Basic examples using the character device API can be found in ``tools/gpio/*``.
The API is based around two major objects, the :ref:`gpio-v2-chip` and the
:ref:`gpio-v2-line-request`.
.. _gpio-v2-chip:
Chip
====
The Chip represents a single GPIO chip and is exposed to userspace using device
files of the form ``/dev/gpiochipX``.
Each chip supports a number of GPIO lines,
:c:type:`chip.lines<gpiochip_info>`. Lines on the chip are identified by an
``offset`` in the range from 0 to ``chip.lines - 1``, i.e. `[0,chip.lines)`.
Lines are requested from the chip using gpio-v2-get-line-ioctl.rst
and the resulting line request is used to access the GPIO chip's lines or
monitor the lines for edge events.
Within this documentation, the file descriptor returned by calling `open()`
on the GPIO device file is referred to as ``chip_fd``.
Operations
----------
The following operations may be performed on the chip:
.. toctree::
:titlesonly:
Get Line <gpio-v2-get-line-ioctl>
Get Chip Info <gpio-get-chipinfo-ioctl>
Get Line Info <gpio-v2-get-lineinfo-ioctl>
Watch Line Info <gpio-v2-get-lineinfo-watch-ioctl>
Unwatch Line Info <gpio-get-lineinfo-unwatch-ioctl>
Read Line Info Changed Events <gpio-v2-lineinfo-changed-read>
.. _gpio-v2-line-request:
Line Request
============
Line requests are created by gpio-v2-get-line-ioctl.rst and provide
access to a set of requested lines. The line request is exposed to userspace
via the anonymous file descriptor returned in
:c:type:`request.fd<gpio_v2_line_request>` by gpio-v2-get-line-ioctl.rst.
Within this documentation, the line request file descriptor is referred to
as ``req_fd``.
Operations
----------
The following operations may be performed on the line request:
.. toctree::
:titlesonly:
Get Line Values <gpio-v2-line-get-values-ioctl>
Set Line Values <gpio-v2-line-set-values-ioctl>
Read Line Edge Events <gpio-v2-line-event-read>
Reconfigure Lines <gpio-v2-line-set-config-ioctl>
Types
=====
This section contains the structs and enums that are referenced by the API v2,
as defined in ``include/uapi/linux/gpio.h``.
.. kernel-doc:: include/uapi/linux/gpio.h
:identifiers:
gpio_v2_line_attr_id
gpio_v2_line_attribute
gpio_v2_line_changed_type
gpio_v2_line_config
gpio_v2_line_config_attribute
gpio_v2_line_event
gpio_v2_line_event_id
gpio_v2_line_flag
gpio_v2_line_info
gpio_v2_line_info_changed
gpio_v2_line_request
gpio_v2_line_values
gpiochip_info
.. toctree::
:hidden:
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