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[PATCH 1/2] v4l2-ctrls: add helper functions for control events.

From: Hans Verkuil <hans.verkuil@xxxxxxxxx>

Many drivers just support control events, and most radio drivers just need
to poll for control events. Add some functions to simplify those jobs.

Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
 drivers/media/video/v4l2-ctrls.c |   20 ++++++++++++++++++++
 include/media/v4l2-ctrls.h       |    9 +++++++++
 2 files changed, 29 insertions(+), 0 deletions(-)

diff --git a/drivers/media/video/v4l2-ctrls.c b/drivers/media/video/v4l2-ctrls.c
index d070688..39829fa 100644
--- a/drivers/media/video/v4l2-ctrls.c
+++ b/drivers/media/video/v4l2-ctrls.c
@@ -2371,3 +2371,23 @@ int v4l2_ctrl_log_status(struct file *file, void *fh)
 	return 0;
+int v4l2_ctrl_subscribe_event(struct v4l2_fh *fh,
+				struct v4l2_event_subscription *sub)
+	if (sub->type == V4L2_EVENT_CTRL)
+		return v4l2_event_subscribe(fh, sub, 0);
+	return -EINVAL;
+unsigned int v4l2_ctrl_poll(struct file *file, struct poll_table_struct *wait)
+	struct v4l2_fh *fh = file->private_data;
+	if (v4l2_event_pending(fh))
+		return POLLPRI;
+	poll_wait(file, &fh->wait, wait);
+	return 0;
diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
index 5f246c2..3dbd066 100644
--- a/include/media/v4l2-ctrls.h
+++ b/include/media/v4l2-ctrls.h
@@ -33,6 +33,7 @@ struct video_device;
 struct v4l2_subdev;
 struct v4l2_subscribed_event;
 struct v4l2_fh;
+struct poll_table_struct;
 /** struct v4l2_ctrl_ops - The control operations that the driver has to provide.
   * @g_volatile_ctrl: Get a new value for this control. Generally only relevant
@@ -496,6 +497,14 @@ void v4l2_ctrl_del_event(struct v4l2_ctrl *ctrl,
    associated with the filehandle. */
 int v4l2_ctrl_log_status(struct file *file, void *fh);
+/* Can be used as a vidioc_subscribe_event function that just subscribes
+   control events. */
+int v4l2_ctrl_subscribe_event(struct v4l2_fh *fh,
+				struct v4l2_event_subscription *sub);
+/* Can be used as a poll function that just polls for control events. */
+unsigned int v4l2_ctrl_poll(struct file *file, struct poll_table_struct *wait);
 /* Helpers for ioctl_ops. If hdl == NULL then they will all return -EINVAL. */
 int v4l2_queryctrl(struct v4l2_ctrl_handler *hdl, struct v4l2_queryctrl *qc);
 int v4l2_querymenu(struct v4l2_ctrl_handler *hdl, struct v4l2_querymenu *qm);

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