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diff --git a/Documentation/media/uapi/v4l/dev-event.rst b/Documentation/media/uapi/v4l/dev-event.rst deleted file mode 100644 index 6029101fe1d7..000000000000 --- a/Documentation/media/uapi/v4l/dev-event.rst +++ /dev/null @@ -1,54 +0,0 @@ -.. Permission is granted to copy, distribute and/or modify this -.. document under the terms of the GNU Free Documentation License, -.. Version 1.1 or any later version published by the Free Software -.. Foundation, with no Invariant Sections, no Front-Cover Texts -.. and no Back-Cover Texts. A copy of the license is included at -.. Documentation/media/uapi/fdl-appendix.rst. -.. -.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections - -.. _event: - -*************** -Event Interface -*************** - -The V4L2 event interface provides a means for a user to get immediately -notified on certain conditions taking place on a device. This might -include start of frame or loss of signal events, for example. Changes in -the value or state of a V4L2 control can also be reported through -events. - -To receive events, the events the user is interested in first must be -subscribed using the -:ref:`VIDIOC_SUBSCRIBE_EVENT` ioctl. Once -an event is subscribed, the events of subscribed types are dequeueable -using the :ref:`VIDIOC_DQEVENT` ioctl. Events may be -unsubscribed using VIDIOC_UNSUBSCRIBE_EVENT ioctl. The special event -type V4L2_EVENT_ALL may be used to unsubscribe all the events the -driver supports. - -The event subscriptions and event queues are specific to file handles. -Subscribing an event on one file handle does not affect other file -handles. - -The information on dequeueable events is obtained by using select or -poll system calls on video devices. The V4L2 events use POLLPRI events -on poll system call and exceptions on select system call. - -Starting with kernel 3.1 certain guarantees can be given with regards to -events: - -1. Each subscribed event has its own internal dedicated event queue. - This means that flooding of one event type will not interfere with - other event types. - -2. If the internal event queue for a particular subscribed event becomes - full, then the oldest event in that queue will be dropped. - -3. Where applicable, certain event types can ensure that the payload of - the oldest event that is about to be dropped will be merged with the - payload of the next oldest event. Thus ensuring that no information - is lost, but only an intermediate step leading up to that - information. See the documentation for the event you want to - subscribe to whether this is applicable for that event or not. |