include/media/v4l2-event.h

   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
  66 struct v4l2_fh;
  67 struct v4l2_subscribed_event;
  68 struct 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   */
  75 struct 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   */
  87 struct 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   */
 107 struct 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
 121 int v4l2_event_dequeue(struct v4l2_fh *fh, struct v4l2_event *event,
 122                        int nonblocking);
 123 void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev);
 124 void v4l2_event_queue_fh(struct v4l2_fh *fh, const struct v4l2_event *ev);
 125 int v4l2_event_pending(struct v4l2_fh *fh);
 126 int v4l2_event_subscribe(struct v4l2_fh *fh,
 127                          struct v4l2_event_subscription *sub, unsigned elems,
 128                          const struct v4l2_subscribed_event_ops *ops);
 129 int v4l2_event_unsubscribe(struct v4l2_fh *fh,
 130                            struct v4l2_event_subscription *sub);
 131 void v4l2_event_unsubscribe_all(struct v4l2_fh *fh);
 132
 133 #endif /* V4L2_EVENT_H */