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+.. SPDX-License-Identifier: GPL-2.0
+
+.. _GPIO_LINEEVENT_DATA_READ:
+
+************************
+GPIO_LINEEVENT_DATA_READ
+************************
+
+.. warning::
+    This ioctl is part of chardev_v1.rst and is obsoleted by
+    gpio-v2-line-event-read.rst.
+
+Name
+====
+
+GPIO_LINEEVENT_DATA_READ - Read edge detection events from a line event.
+
+Synopsis
+========
+
+``int read(int event_fd, void *buf, size_t count)``
+
+Arguments
+=========
+
+``event_fd``
+    The file descriptor of the GPIO character device, as returned in the
+    :c:type:`request.fd<gpioevent_request>` by gpio-get-lineevent-ioctl.rst.
+
+``buf``
+    The buffer to contain the :c:type:`events<gpioevent_data>`.
+
+``count``
+    The number of bytes available in ``buf``, which must be at
+    least the size of a :c:type:`gpioevent_data`.
+
+Description
+===========
+
+Read edge detection events for a line from a line event.
+
+Edge detection must be enabled for the input line using either
+``GPIOEVENT_REQUEST_RISING_EDGE`` or ``GPIOEVENT_REQUEST_FALLING_EDGE``, or
+both. Edge events are then generated whenever edge interrupts are detected on
+the input line.
+
+The kernel captures and timestamps edge events as close as possible to their
+occurrence and stores them in a buffer from where they can be read by
+userspace at its convenience using `read()`.
+
+The source of the clock for :c:type:`event.timestamp<gpioevent_data>` is
+``CLOCK_MONOTONIC``, except for kernels earlier than Linux 5.7 when it was
+``CLOCK_REALTIME``.  There is no indication in the :c:type:`gpioevent_data`
+as to which clock source is used, it must be determined from either the kernel
+version or sanity checks on the timestamp itself.
+
+Events read from the buffer are always in the same order that they were
+detected by the kernel.
+
+The size of the kernel event buffer is fixed at 16 events.
+
+The buffer may overflow if bursts of events occur quicker than they are read
+by userspace. If an overflow occurs then the most recent event is discarded.
+Overflow cannot be detected from userspace.
+
+To minimize the number of calls required to copy events from the kernel to
+userspace, `read()` supports copying multiple events. The number of events
+copied is the lower of the number available in the kernel buffer and the
+number that will fit in the userspace buffer (``buf``).
+
+The `read()` will block if no event is available and the ``event_fd`` has not
+been set **O_NONBLOCK**.
+
+The presence of an event can be tested for by checking that the ``event_fd`` is
+readable using `poll()` or an equivalent.
+
+Return Value
+============
+
+On success the number of bytes read, which will be a multiple of the size of
+a :c:type:`gpio_lineevent_data` event.
+
+On error -1 and the ``errno`` variable is set appropriately.
+Common error codes are described in error-codes.rst.