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16b2bb7fe5
Add documentation for v1 of the GPIO character device userspace API to the obsolete section of both the admin-guide and userspace-api books. Signed-off-by: Kent Gibson <warthog618@gmail.com> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
75 lines
2.1 KiB
ReStructuredText
75 lines
2.1 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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.. _GPIO_GET_LINEINFO_WATCH_IOCTL:
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*****************************
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GPIO_GET_LINEINFO_WATCH_IOCTL
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*****************************
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.. warning::
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This ioctl is part of chardev_v1.rst and is obsoleted by
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gpio-v2-get-lineinfo-watch-ioctl.rst.
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Name
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====
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GPIO_GET_LINEINFO_WATCH_IOCTL - Enable watching a line for changes to its
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request state and configuration information.
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Synopsis
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========
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.. c:macro:: GPIO_GET_LINEINFO_WATCH_IOCTL
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``int ioctl(int chip_fd, GPIO_GET_LINEINFO_WATCH_IOCTL, struct gpioline_info *info)``
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Arguments
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=========
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``chip_fd``
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The file descriptor of the GPIO character device returned by `open()`.
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``info``
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The :c:type:`line_info<gpioline_info>` struct to be populated, with
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the ``offset`` set to indicate the line to watch
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Description
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===========
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Enable watching a line for changes to its request state and configuration
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information. Changes to line info include a line being requested, released
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or reconfigured.
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.. note::
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Watching line info is not generally required, and would typically only be
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used by a system monitoring component.
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The line info does NOT include the line value.
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The line must be requested using gpio-get-linehandle-ioctl.rst or
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gpio-get-lineevent-ioctl.rst to access its value, and the line event can
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monitor a line for events using gpio-lineevent-data-read.rst.
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By default all lines are unwatched when the GPIO chip is opened.
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Multiple lines may be watched simultaneously by adding a watch for each.
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Once a watch is set, any changes to line info will generate events which can be
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read from the ``chip_fd`` as described in
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gpio-lineinfo-changed-read.rst.
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Adding a watch to a line that is already watched is an error (**EBUSY**).
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Watches are specific to the ``chip_fd`` and are independent of watches
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on the same GPIO chip opened with a separate call to `open()`.
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First added in 5.7.
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Return Value
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============
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On success 0 and ``info`` is populated with the current line info.
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On error -1 and the ``errno`` variable is set appropriately.
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Common error codes are described in error-codes.rst.
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