diff options
authorHans Verkuil <hans.verkuil@cisco.com>2012-09-07 04:46:39 -0300
committerMauro Carvalho Chehab <mchehab@redhat.com>2013-01-05 00:49:54 -0200
commit8ac7a9493a4380a8a886fbfe311ab00bc424ca0f (patch)
parent20deebfe17b20ded00ba404adbcd014eb2b024c1 (diff)
[media] v4l2-ctrls: add a notify callback
Sometimes platform/bridge drivers need to be notified when a control from a sub-device changes value. In order to support this a notify callback was added. [dheitmueller@kernellabs.com: fix merge conflict in v4l2-ctrls.c] Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
3 files changed, 57 insertions, 8 deletions
diff --git a/Documentation/video4linux/v4l2-controls.txt b/Documentation/video4linux/v4l2-controls.txt
index cfe52c798d74..676f87366025 100644
--- a/Documentation/video4linux/v4l2-controls.txt
+++ b/Documentation/video4linux/v4l2-controls.txt
@@ -715,14 +715,20 @@ a control of this type whenever the first control belonging to a new control
class is added.
-Proposals for Extensions
+Adding Notify Callbacks
+Sometimes the platform or bridge driver needs to be notified when a control
+from a sub-device driver changes. You can set a notify callback by calling
+this function:
-Some ideas for future extensions to the spec:
+void v4l2_ctrl_notify(struct v4l2_ctrl *ctrl,
+ void (*notify)(struct v4l2_ctrl *ctrl, void *priv), void *priv);
-1) Add a V4L2_CTRL_FLAG_HEX to have values shown as hexadecimal instead of
-decimal. Useful for e.g. video_mute_yuv.
+Whenever the give control changes value the notify callback will be called
+with a pointer to the control and the priv pointer that was passed with
+v4l2_ctrl_notify. Note that the control's handler lock is held when the
+notify function is called.
-2) It is possible to mark in the controls array which controls have been
-successfully written and which failed by for example adding a bit to the
-control ID. Not sure if it is worth the effort, though.
+There can be only one notify function per control handler. Any attempt
+to set another notify function will cause a WARN_ON.
diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
index f6ee201d9347..fa02363e7db4 100644
--- a/drivers/media/v4l2-core/v4l2-ctrls.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls.c
@@ -1204,6 +1204,8 @@ static void new_to_cur(struct v4l2_fh *fh, struct v4l2_ctrl *ctrl,
send_event(fh, ctrl,
(changed ? V4L2_EVENT_CTRL_CH_VALUE : 0) |
(update_inactive ? V4L2_EVENT_CTRL_CH_FLAGS : 0));
+ if (ctrl->call_notify && changed && ctrl->handler->notify)
+ ctrl->handler->notify(ctrl, ctrl->handler->notify_priv);
@@ -2725,6 +2727,22 @@ int v4l2_ctrl_s_ctrl_int64(struct v4l2_ctrl *ctrl, s64 val)
+void v4l2_ctrl_notify(struct v4l2_ctrl *ctrl, v4l2_ctrl_notify_fnc notify, void *priv)
+ if (ctrl == NULL)
+ return;
+ if (notify == NULL) {
+ ctrl->call_notify = 0;
+ return;
+ }
+ if (WARN_ON(ctrl->handler->notify && ctrl->handler->notify != notify))
+ return;
+ ctrl->handler->notify = notify;
+ ctrl->handler->notify_priv = priv;
+ ctrl->call_notify = 1;
static int v4l2_ctrl_add_event(struct v4l2_subscribed_event *sev, unsigned elems)
struct v4l2_ctrl *ctrl = v4l2_ctrl_find(sev->fh->ctrl_handler, sev->id);
diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
index 96509119f28f..c4cc04136074 100644
--- a/include/media/v4l2-ctrls.h
+++ b/include/media/v4l2-ctrls.h
@@ -53,6 +53,8 @@ struct v4l2_ctrl_ops {
int (*s_ctrl)(struct v4l2_ctrl *ctrl);
+typedef void (*v4l2_ctrl_notify_fnc)(struct v4l2_ctrl *ctrl, void *priv);
/** struct v4l2_ctrl - The control structure.
* @node: The list node.
* @ev_subs: The list of control event subscriptions.
@@ -72,6 +74,8 @@ struct v4l2_ctrl_ops {
* set this flag directly.
* @has_volatiles: If set, then one or more members of the cluster are volatile.
* Drivers should never touch this flag.
+ * @call_notify: If set, then call the handler's notify function whenever the
+ * control's value changes.
* @manual_mode_value: If the is_auto flag is set, then this is the value
* of the auto control that determines if that control is in
* manual mode. So if the value of the auto control equals this
@@ -119,6 +123,7 @@ struct v4l2_ctrl {
unsigned int is_private:1;
unsigned int is_auto:1;
unsigned int has_volatiles:1;
+ unsigned int call_notify:1;
unsigned int manual_mode_value:8;
const struct v4l2_ctrl_ops *ops;
@@ -177,6 +182,10 @@ struct v4l2_ctrl_ref {
* control is needed multiple times, so this is a simple
* optimization.
* @buckets: Buckets for the hashing. Allows for quick control lookup.
+ * @notify: A notify callback that is called whenever the control changes value.
+ * Note that the handler's lock is held when the notify function
+ * is called!
+ * @notify_priv: Passed as argument to the v4l2_ctrl notify callback.
* @nr_of_buckets: Total number of buckets in the array.
* @error: The error code of the first failed control addition.
@@ -187,6 +196,8 @@ struct v4l2_ctrl_handler {
struct list_head ctrl_refs;
struct v4l2_ctrl_ref *cached;
struct v4l2_ctrl_ref **buckets;
+ v4l2_ctrl_notify_fnc notify;
+ void *notify_priv;
u16 nr_of_buckets;
int error;
@@ -525,6 +536,20 @@ static inline void v4l2_ctrl_unlock(struct v4l2_ctrl *ctrl)
+/** v4l2_ctrl_notify() - Function to set a notify callback for a control.
+ * @ctrl: The control.
+ * @notify: The callback function.
+ * @priv: The callback private handle, passed as argument to the callback.
+ *
+ * This function sets a callback function for the control. If @ctrl is NULL,
+ * then it will do nothing. If @notify is NULL, then the notify callback will
+ * be removed.
+ *
+ * There can be only one notify. If another already exists, then a WARN_ON
+ * will be issued and the function will do nothing.
+ */
+void v4l2_ctrl_notify(struct v4l2_ctrl *ctrl, v4l2_ctrl_notify_fnc notify, void *priv);
/** v4l2_ctrl_g_ctrl() - Helper function to get the control's value from within a driver.
* @ctrl: The control.

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