From 9f0346dcbea363787186c94ef94dd01aaa215afa Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 5 Sep 2026 11:59:05 -0700 Subject: Merge tag 'driver-core-7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core Pull driver core fixes from Danilo Krummrich: - Fix kernfs listxattr() not returning security xattr names (e.g. SELinux labels) when the kernfs node has no allocated kernfs_iattrs - Fix silent truncation of IRQ vector indices in the Rust PCI abstractions - Don't select OF from DRIVER_PE_KUNIT_TEST; skip the test when OF is disabled instead of silently enabling extra kernel functionality - Russ Weight is retiring from kernel development; update the Firmware Loader sysfs contact to the driver-core mailing list, add a CREDITS entry for Firmware Upload, and update MAINTAINERS accordingly * tag 'driver-core-7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core: MAINTAINERS: Remove Russ Weight from Firmware Loader CREDITS: Add CREDITS entry for Firmware Upload firmware_loader: Change contact for sysfs nodes rust: pci: reject IRQ vector indices that do not fit in u32 kernfs: preserve security xattrs without allocating iattrs drivers: base: test: DRIVER_PE_KUNIT_TEST should not select OF --- Documentation/userspace-api/gpio/chardev.rst | 116 +++++++++++++++++++++++++++ 1 file changed, 116 insertions(+) create mode 100644 Documentation/userspace-api/gpio/chardev.rst (limited to 'Documentation/userspace-api/gpio/chardev.rst') diff --git a/Documentation/userspace-api/gpio/chardev.rst b/Documentation/userspace-api/gpio/chardev.rst new file mode 100644 index 000000000..c58dd9771 --- /dev/null +++ b/Documentation/userspace-api/gpio/chardev.rst @@ -0,0 +1,116 @@ +.. 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`. 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 + Get Chip Info + Get Line Info + Watch Line Info + Unwatch Line Info + Read Line Info Changed Events + +.. _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` 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 + Set Line Values + Read Line Edge Events + Reconfigure Lines + +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: + + error-codes -- cgit v1.3.1