linux/include/media/v4l2-event.h

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/*
* 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;
[media] v4l2-event/ctrls/fh: allocate events per fh and per type instead of just per-fh The driver had to decide how many events to allocate when the v4l2_fh struct was created. It was possible to add more events afterwards, but there was no way to ensure that you wouldn't miss important events if the event queue would fill up for that filehandle. In addition, once there were no more free events, any new events were simply dropped on the floor. For the control event in particular this made life very difficult since control status/value changes could just be missed if the number of allocated events and the speed at which the application read events was too low to keep up with the number of generated events. The application would have no idea what the latest state was for a control since it could have missed the latest control change. So this patch makes some major changes in how events are allocated. Instead of allocating events per-filehandle they are now allocated when subscribing an event. So for that particular event type N events (determined by the driver) are allocated. Those events are reserved for that particular event type. This ensures that you will not miss events for a particular type altogether. In addition, if there are N events in use and a new event is raised, then the oldest event is dropped and the new one is added. So the latest event is always available. This can be further improved by adding the ability to merge the state of two events together, ensuring that no data is lost at all. This will be added in the next patch. This also makes it possible to allow the user to determine the number of events that will be allocated. This is not implemented at the moment, but would be trivial. Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
2011-06-14 06:24:17 +08:00
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;
[media] v4l2-event/ctrls/fh: allocate events per fh and per type instead of just per-fh The driver had to decide how many events to allocate when the v4l2_fh struct was created. It was possible to add more events afterwards, but there was no way to ensure that you wouldn't miss important events if the event queue would fill up for that filehandle. In addition, once there were no more free events, any new events were simply dropped on the floor. For the control event in particular this made life very difficult since control status/value changes could just be missed if the number of allocated events and the speed at which the application read events was too low to keep up with the number of generated events. The application would have no idea what the latest state was for a control since it could have missed the latest control change. So this patch makes some major changes in how events are allocated. Instead of allocating events per-filehandle they are now allocated when subscribing an event. So for that particular event type N events (determined by the driver) are allocated. Those events are reserved for that particular event type. This ensures that you will not miss events for a particular type altogether. In addition, if there are N events in use and a new event is raised, then the oldest event is dropped and the new one is added. So the latest event is always available. This can be further improved by adding the ability to merge the state of two events together, ensuring that no data is lost at all. This will be added in the next patch. This also makes it possible to allow the user to determine the number of events that will be allocated. This is not implemented at the moment, but would be trivial. Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
2011-06-14 06:24:17 +08:00
struct v4l2_subscribed_event *sev;
struct v4l2_event event;
};
/** struct v4l2_subscribed_event_ops - Subscribed event operations.
* @add: Optional callback, called when a new listener is added
* @del: Optional callback, called when a listener stops listening
* @replace: Optional callback that can replace event 'old' with event 'new'.
* @merge: Optional callback that can merge event 'old' into event 'new'.
*/
struct v4l2_subscribed_event_ops {
int (*add)(struct v4l2_subscribed_event *sev, unsigned elems);
void (*del)(struct v4l2_subscribed_event *sev);
void (*replace)(struct v4l2_event *old, const struct v4l2_event *new);
void (*merge)(const struct v4l2_event *old, struct v4l2_event *new);
};
/** 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).
* @ops: v4l2_subscribed_event_ops
* @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;
const struct v4l2_subscribed_event_ops *ops;
[media] v4l2-event/ctrls/fh: allocate events per fh and per type instead of just per-fh The driver had to decide how many events to allocate when the v4l2_fh struct was created. It was possible to add more events afterwards, but there was no way to ensure that you wouldn't miss important events if the event queue would fill up for that filehandle. In addition, once there were no more free events, any new events were simply dropped on the floor. For the control event in particular this made life very difficult since control status/value changes could just be missed if the number of allocated events and the speed at which the application read events was too low to keep up with the number of generated events. The application would have no idea what the latest state was for a control since it could have missed the latest control change. So this patch makes some major changes in how events are allocated. Instead of allocating events per-filehandle they are now allocated when subscribing an event. So for that particular event type N events (determined by the driver) are allocated. Those events are reserved for that particular event type. This ensures that you will not miss events for a particular type altogether. In addition, if there are N events in use and a new event is raised, then the oldest event is dropped and the new one is added. So the latest event is always available. This can be further improved by adding the ability to merge the state of two events together, ensuring that no data is lost at all. This will be added in the next patch. This also makes it possible to allow the user to determine the number of events that will be allocated. This is not implemented at the moment, but would be trivial. Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
2011-06-14 06:24:17 +08:00
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,
const struct v4l2_event_subscription *sub, unsigned elems,
const struct v4l2_subscribed_event_ops *ops);
int v4l2_event_unsubscribe(struct v4l2_fh *fh,
const struct v4l2_event_subscription *sub);
[media] v4l2-event/ctrls/fh: allocate events per fh and per type instead of just per-fh The driver had to decide how many events to allocate when the v4l2_fh struct was created. It was possible to add more events afterwards, but there was no way to ensure that you wouldn't miss important events if the event queue would fill up for that filehandle. In addition, once there were no more free events, any new events were simply dropped on the floor. For the control event in particular this made life very difficult since control status/value changes could just be missed if the number of allocated events and the speed at which the application read events was too low to keep up with the number of generated events. The application would have no idea what the latest state was for a control since it could have missed the latest control change. So this patch makes some major changes in how events are allocated. Instead of allocating events per-filehandle they are now allocated when subscribing an event. So for that particular event type N events (determined by the driver) are allocated. Those events are reserved for that particular event type. This ensures that you will not miss events for a particular type altogether. In addition, if there are N events in use and a new event is raised, then the oldest event is dropped and the new one is added. So the latest event is always available. This can be further improved by adding the ability to merge the state of two events together, ensuring that no data is lost at all. This will be added in the next patch. This also makes it possible to allow the user to determine the number of events that will be allocated. This is not implemented at the moment, but would be trivial. Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
2011-06-14 06:24:17 +08:00
void v4l2_event_unsubscribe_all(struct v4l2_fh *fh);
#endif /* V4L2_EVENT_H */