On Wed, Jun 29, 2011 at 02:00:37PM +0200, Hans Verkuil wrote:
> Hi all,
Hi Hans,
Thanks for the patch.
Just one comment. I guess it's not strict in DocBook but many of the lines
are well over 80 characters. The paragraphs especially would be easier read
when wrapped around that column. I could also be I'm the only one whose
$COLUMNS == 80. :-)
> Second attempt: inverted the meaning of the flag as per Laurent's suggestion.
>
> Regards,
>
> Hans
>
>
>
> Normally no control events will go to the filehandle that called the
> VIDIOC_S_CTRL/VIDIOC_S_EXT_CTRLS ioctls. This is to prevent a feedback
> loop.
>
> This can now be overridden by setting the new V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK
> flag.
>
> Based on suggestions from Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> and
> Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>.
>
> Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
> ---
> .../DocBook/media/v4l/vidioc-subscribe-event.xml | 36 ++++++++++++++++----
> drivers/media/video/v4l2-ctrls.c | 3 +-
> include/linux/videodev2.h | 3 +-
> 3 files changed, 33 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml b/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml
> index 039a969..25471e8 100644
> --- a/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml
> +++ b/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml
> @@ -114,25 +114,28 @@
> <row>
> <entry><constant>V4L2_EVENT_CTRL</constant></entry>
> <entry>3</entry>
> - <entry>This event requires that the <structfield>id</structfield>
> + <entry><para>This event requires that the <structfield>id</structfield>
> matches the control ID from which you want to receive events.
> This event is triggered if the control's value changes, if a
> button control is pressed or if the control's flags change.
> This event has a &v4l2-event-ctrl; associated with it. This struct
> contains much of the same information as &v4l2-queryctrl; and
> - &v4l2-control;.
> + &v4l2-control;.</para>
>
> - If the event is generated due to a call to &VIDIOC-S-CTRL; or
> - &VIDIOC-S-EXT-CTRLS;, then the event will not be sent to
> + <para>If the event is generated due to a call to &VIDIOC-S-CTRL; or
> + &VIDIOC-S-EXT-CTRLS;, then the event will <emphasis>not</emphasis> be sent to
> the file handle that called the ioctl function. This prevents
> - nasty feedback loops.
> + nasty feedback loops. If you <emphasis>do</emphasis> want to get the
> + event, then set the <constant>V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK</constant>
> + flag.
> + </para>
>
> - This event type will ensure that no information is lost when
> + <para>This event type will ensure that no information is lost when
> more events are raised than there is room internally. In that
> case the &v4l2-event-ctrl; of the second-oldest event is kept,
> but the <structfield>changes</structfield> field of the
> second-oldest event is ORed with the <structfield>changes</structfield>
> - field of the oldest event.
> + field of the oldest event.</para>
> </entry>
> </row>
> <row>
> @@ -157,6 +160,25 @@
> that are triggered by a status change such as <constant>V4L2_EVENT_CTRL</constant>.
> Other events will ignore this flag.</entry>
> </row>
> + <row>
> + <entry><constant>V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK</constant></entry>
> + <entry>0x0002</entry>
> + <entry><para>If set, then events directly caused by an ioctl will also be sent to
> + the filehandle that called that ioctl. For example, changing a control using
> + &VIDIOC-S-CTRL; will cause a V4L2_EVENT_CTRL to be sent back to that same
> + filehandle. Normally such events are suppressed to prevent feedback loops
> + where an application changes a control to a one value and then another, and
> + then receives an event telling it that that control has changed to the first
> + value.</para>
> +
> + <para>Since it can't tell whether that event was caused by another application
> + or by the &VIDIOC-S-CTRL; call it is hard to decide whether to set the
> + control to the value in the event, or ignore it.</para>
> +
> + <para>Think carefully when you set this flag so you won't get into situations
> + like that.</para>
> + </entry>
> + </row>
> </tbody>
> </tgroup>
> </table>
> diff --git a/drivers/media/video/v4l2-ctrls.c b/drivers/media/video/v4l2-ctrls.c
> index bc08f86..bd2456d 100644
> --- a/drivers/media/video/v4l2-ctrls.c
> +++ b/drivers/media/video/v4l2-ctrls.c
> @@ -590,7 +590,8 @@ static void send_event(struct v4l2_fh *fh, struct v4l2_ctrl *ctrl, u32 changes)
> fill_event(&ev, ctrl, changes);
>
> list_for_each_entry(sev, &ctrl->ev_subs, node)
> - if (sev->fh && sev->fh != fh)
> + if (sev->fh && (sev->fh != fh ||
> + (sev->flags & V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK)))
> v4l2_event_queue_fh(sev->fh, &ev);
> }
>
> diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
> index baafe2f..2c4e837 100644
> --- a/include/linux/videodev2.h
> +++ b/include/linux/videodev2.h
> @@ -1832,7 +1832,8 @@ struct v4l2_event {
> __u32 reserved[8];
> };
>
> -#define V4L2_EVENT_SUB_FL_SEND_INITIAL (1 << 0)
> +#define V4L2_EVENT_SUB_FL_SEND_INITIAL (1 << 0)
> +#define V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK (1 << 1)
>
> struct v4l2_event_subscription {
> __u32 type;
> --
> 1.7.1
>
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--
Sakari Ailus
sakari.ailus@xxxxxx
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