68 lines
1.9 KiB
ReStructuredText
68 lines
1.9 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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.. _GPIO_V2_GET_LINEINFO_WATCH_IOCTL:
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********************************
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GPIO_V2_GET_LINEINFO_WATCH_IOCTL
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********************************
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Name
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====
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GPIO_V2_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_V2_GET_LINEINFO_WATCH_IOCTL
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``int ioctl(int chip_fd, GPIO_V2_GET_LINEINFO_WATCH_IOCTL, struct gpio_v2_line_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<gpio_v2_line_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-v2-get-line-ioctl.rst to access
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its value, and the line request can monitor a line for events using
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gpio-v2-line-event-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-v2-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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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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