linux/include/media/v4l2-event.h
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   1/*
   2 * v4l2-event.h
   3 *
   4 * V4L2 events.
   5 *
   6 * Copyright (C) 2009--2010 Nokia Corporation.
   7 *
   8 * Contact: Sakari Ailus <sakari.ailus@maxwell.research.nokia.com>
   9 *
  10 * This program is free software; you can redistribute it and/or
  11 * modify it under the terms of the GNU General Public License
  12 * version 2 as published by the Free Software Foundation.
  13 *
  14 * This program is distributed in the hope that it will be useful, but
  15 * WITHOUT ANY WARRANTY; without even the implied warranty of
  16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17 * General Public License for more details.
  18 *
  19 * You should have received a copy of the GNU General Public License
  20 * along with this program; if not, write to the Free Software
  21 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
  22 * 02110-1301 USA
  23 */
  24
  25#ifndef V4L2_EVENT_H
  26#define V4L2_EVENT_H
  27
  28#include <linux/types.h>
  29#include <linux/videodev2.h>
  30#include <linux/wait.h>
  31
  32/*
  33 * Overview:
  34 *
  35 * Events are subscribed per-filehandle. An event specification consists of a
  36 * type and is optionally associated with an object identified through the
  37 * 'id' field. So an event is uniquely identified by the (type, id) tuple.
  38 *
  39 * The v4l2-fh struct has a list of subscribed events. The v4l2_subscribed_event
  40 * struct is added to that list, one for every subscribed event.
  41 *
  42 * Each v4l2_subscribed_event struct ends with an array of v4l2_kevent structs.
  43 * This array (ringbuffer, really) is used to store any events raised by the
  44 * driver. The v4l2_kevent struct links into the 'available' list of the
  45 * v4l2_fh struct so VIDIOC_DQEVENT will know which event to dequeue first.
  46 *
  47 * Finally, if the event subscription is associated with a particular object
  48 * such as a V4L2 control, then that object needs to know about that as well
  49 * so that an event can be raised by that object. So the 'node' field can
  50 * be used to link the v4l2_subscribed_event struct into a list of that
  51 * object.
  52 *
  53 * So to summarize:
  54 *
  55 * struct v4l2_fh has two lists: one of the subscribed events, and one of the
  56 * pending events.
  57 *
  58 * struct v4l2_subscribed_event has a ringbuffer of raised (pending) events of
  59 * that particular type.
  60 *
  61 * If struct v4l2_subscribed_event is associated with a specific object, then
  62 * that object will have an internal list of struct v4l2_subscribed_event so
  63 * it knows who subscribed an event to that object.
  64 */
  65
  66struct v4l2_fh;
  67struct v4l2_subscribed_event;
  68struct video_device;
  69
  70/** struct v4l2_kevent - Internal kernel event struct.
  71  * @list:      List node for the v4l2_fh->available list.
  72  * @sev:       Pointer to parent v4l2_subscribed_event.
  73  * @event:     The event itself.
  74  */
  75struct v4l2_kevent {
  76        struct list_head        list;
  77        struct v4l2_subscribed_event *sev;
  78        struct v4l2_event       event;
  79};
  80
  81/** struct v4l2_subscribed_event_ops - Subscribed event operations.
  82  * @add:       Optional callback, called when a new listener is added
  83  * @del:       Optional callback, called when a listener stops listening
  84  * @replace:   Optional callback that can replace event 'old' with event 'new'.
  85  * @merge:     Optional callback that can merge event 'old' into event 'new'.
  86  */
  87struct v4l2_subscribed_event_ops {
  88        int  (*add)(struct v4l2_subscribed_event *sev, unsigned elems);
  89        void (*del)(struct v4l2_subscribed_event *sev);
  90        void (*replace)(struct v4l2_event *old, const struct v4l2_event *new);
  91        void (*merge)(const struct v4l2_event *old, struct v4l2_event *new);
  92};
  93
  94/** struct v4l2_subscribed_event - Internal struct representing a subscribed event.
  95  * @list:      List node for the v4l2_fh->subscribed list.
  96  * @type:      Event type.
  97  * @id:        Associated object ID (e.g. control ID). 0 if there isn't any.
  98  * @flags:     Copy of v4l2_event_subscription->flags.
  99  * @fh:        Filehandle that subscribed to this event.
 100  * @node:      List node that hooks into the object's event list (if there is one).
 101  * @ops:       v4l2_subscribed_event_ops
 102  * @elems:     The number of elements in the events array.
 103  * @first:     The index of the events containing the oldest available event.
 104  * @in_use:    The number of queued events.
 105  * @events:    An array of @elems events.
 106  */
 107struct v4l2_subscribed_event {
 108        struct list_head        list;
 109        u32                     type;
 110        u32                     id;
 111        u32                     flags;
 112        struct v4l2_fh          *fh;
 113        struct list_head        node;
 114        const struct v4l2_subscribed_event_ops *ops;
 115        unsigned                elems;
 116        unsigned                first;
 117        unsigned                in_use;
 118        struct v4l2_kevent      events[];
 119};
 120
 121int v4l2_event_dequeue(struct v4l2_fh *fh, struct v4l2_event *event,
 122                       int nonblocking);
 123void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev);
 124void v4l2_event_queue_fh(struct v4l2_fh *fh, const struct v4l2_event *ev);
 125int v4l2_event_pending(struct v4l2_fh *fh);
 126int v4l2_event_subscribe(struct v4l2_fh *fh,
 127                         struct v4l2_event_subscription *sub, unsigned elems,
 128                         const struct v4l2_subscribed_event_ops *ops);
 129int v4l2_event_unsubscribe(struct v4l2_fh *fh,
 130                           struct v4l2_event_subscription *sub);
 131void v4l2_event_unsubscribe_all(struct v4l2_fh *fh);
 132
 133#endif /* V4L2_EVENT_H */
 134
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