/*
   * v4l2-event.h
   *
   * V4L2 events.
   *
   * Copyright (C) 2009--2010 Nokia Corporation.
   *
   * Contact: Sakari Ailus <sakari.ailus@maxwell.research.nokia.com>
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * version 2 as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
   * 02110-1301 USA
   */
  
  #ifndef V4L2_EVENT_H
  #define V4L2_EVENT_H
  
  #include <linux/types.h>
  #include <linux/videodev2.h>
  #include <linux/wait.h>

  /*
   * Overview:
   *
   * Events are subscribed per-filehandle. An event specification consists of a
   * type and is optionally associated with an object identified through the
   * 'id' field. So an event is uniquely identified by the (type, id) tuple.
   *
   * The v4l2-fh struct has a list of subscribed events. The v4l2_subscribed_event
   * struct is added to that list, one for every subscribed event.
   *
   * Each v4l2_subscribed_event struct ends with an array of v4l2_kevent structs.
   * This array (ringbuffer, really) is used to store any events raised by the
   * driver. The v4l2_kevent struct links into the 'available' list of the
   * v4l2_fh struct so VIDIOC_DQEVENT will know which event to dequeue first.
   *
   * Finally, if the event subscription is associated with a particular object
   * such as a V4L2 control, then that object needs to know about that as well
   * so that an event can be raised by that object. So the 'node' field can
   * be used to link the v4l2_subscribed_event struct into a list of that
   * object.
   *
   * So to summarize:
   *
   * struct v4l2_fh has two lists: one of the subscribed events, and one of the
   * pending events.
   *
   * struct v4l2_subscribed_event has a ringbuffer of raised (pending) events of
   * that particular type.
   *
   * If struct v4l2_subscribed_event is associated with a specific object, then
   * that object will have an internal list of struct v4l2_subscribed_event so
   * it knows who subscribed an event to that object.
   */

  struct v4l2_fh;

  struct v4l2_subscribed_event;

  struct video_device;

  /** struct v4l2_kevent - Internal kernel event struct.
    * @list:	List node for the v4l2_fh->available list.
    * @sev:	Pointer to parent v4l2_subscribed_event.
    * @event:	The event itself.
    */

  struct v4l2_kevent {
  	struct list_head	list;

  	struct v4l2_subscribed_event *sev;

  	struct v4l2_event	event;
  };

  /** struct v4l2_subscribed_event - Internal struct representing a subscribed event.
    * @list:	List node for the v4l2_fh->subscribed list.
    * @type:	Event type.
    * @id:	Associated object ID (e.g. control ID). 0 if there isn't any.
    * @flags:	Copy of v4l2_event_subscription->flags.
    * @fh:	Filehandle that subscribed to this event.
    * @node:	List node that hooks into the object's event list (if there is one).
    * @replace:	Optional callback that can replace event 'old' with event 'new'.
    * @merge:	Optional callback that can merge event 'old' into event 'new'.
    * @elems:	The number of elements in the events array.
    * @first:	The index of the events containing the oldest available event.
    * @in_use:	The number of queued events.
    * @events:	An array of @elems events.
    */

  struct v4l2_subscribed_event {
  	struct list_head	list;
  	u32			type;

  	u32			id;

  	u32			flags;

  	struct v4l2_fh		*fh;

  	struct list_head	node;

  	void			(*replace)(struct v4l2_event *old,
  					   const struct v4l2_event *new);

  	void			(*merge)(const struct v4l2_event *old,
  					 struct v4l2_event *new);

  	unsigned		elems;

  	unsigned		first;

  	unsigned		in_use;

  	struct v4l2_kevent	events[];

  };

  int v4l2_event_dequeue(struct v4l2_fh *fh, struct v4l2_event *event,
  		       int nonblocking);
  void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev);

  void v4l2_event_queue_fh(struct v4l2_fh *fh, const struct v4l2_event *ev);

  int v4l2_event_pending(struct v4l2_fh *fh);
  int v4l2_event_subscribe(struct v4l2_fh *fh,

  			 struct v4l2_event_subscription *sub, unsigned elems);

  int v4l2_event_unsubscribe(struct v4l2_fh *fh,
  			   struct v4l2_event_subscription *sub);

  void v4l2_event_unsubscribe_all(struct v4l2_fh *fh);

  
  #endif /* V4L2_EVENT_H */