linux-kernel - Re: [PATCH 1/2] [media] V4L: Add camera pan/tilt speed controls

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Date:	Fri, 8 Aug 2014 09:41:00 -0700
From:	Vincent Palatin <vpalatin@...omium.org>
To:	Pawel Osciak <posciak@...omium.org>
Cc:	Hans de Goede <hdegoede@...hat.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Olof Johansson <olofj@...omium.org>,
	Zach Kuznia <zork@...omium.org>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>
Subject: Re: [PATCH 1/2] [media] V4L: Add camera pan/tilt speed controls

On Wed, Aug 6, 2014 at 7:18 PM, Pawel Osciak <posciak@...omium.org> wrote:
>
> On Thu, Aug 7, 2014 at 12:10 AM, Vincent Palatin <vpalatin@...omium.org> wrote:
> >
> > On Sun, Aug 3, 2014 at 10:52 PM, Pawel Osciak <posciak@...omium.org> wrote:
> > > This looks good to me in general (with one comment below). I don't think we
> > > can easily implement current V4L2 pan and tilt controls that are for
> > > movement by a specified amount in terms of UVC pan/tilt speed controls,
> > > which only let us set speed and direction...
> > >
> > > On Wed, Jul 9, 2014 at 8:49 AM, Vincent Palatin <vpalatin@...omium.org>
> > > wrote:
> > >>
> > >> The V4L2_CID_PAN_SPEED and V4L2_CID_TILT_SPEED controls allow to move the
> > >> camera by setting its rotation speed around its axis.
> > >>
> > >> Signed-off-by: Vincent Palatin <vpalatin@...omium.org>
> > >>
> > >> ---
> > >>  Documentation/DocBook/media/v4l/compat.xml   | 10 ++++++++++
> > >>  Documentation/DocBook/media/v4l/controls.xml | 21 +++++++++++++++++++++
> > >>  drivers/media/v4l2-core/v4l2-ctrls.c         |  2 ++
> > >>  include/uapi/linux/v4l2-controls.h           |  2 ++
> > >>  4 files changed, 35 insertions(+)
> > >>
> > >> diff --git a/Documentation/DocBook/media/v4l/compat.xml
> > >> b/Documentation/DocBook/media/v4l/compat.xml
> > >> index eee6f0f..21910e9 100644
> > >> --- a/Documentation/DocBook/media/v4l/compat.xml
> > >> +++ b/Documentation/DocBook/media/v4l/compat.xml
> > >> @@ -2545,6 +2545,16 @@ fields changed from _s32 to _u32.
> > >>        </orderedlist>
> > >>      </section>
> > >>
> > >> +    <section>
> > >> +      <title>V4L2 in Linux 3.17</title>
> > >> +      <orderedlist>
> > >> +       <listitem>
> > >> +         <para>Added <constant>V4L2_CID_PAN_SPEED</constant> and
> > >> + <constant>V4L2_CID_TILT_SPEED</constant> camera controls.</para>
> > >> +       </listitem>
> > >> +      </orderedlist>
> > >> +    </section>
> > >> +
> > >>      <section id="other">
> > >>        <title>Relation of V4L2 to other Linux multimedia APIs</title>
> > >>
> > >> diff --git a/Documentation/DocBook/media/v4l/controls.xml
> > >> b/Documentation/DocBook/media/v4l/controls.xml
> > >> index 47198ee..cdf97f0 100644
> > >> --- a/Documentation/DocBook/media/v4l/controls.xml
> > >> +++ b/Documentation/DocBook/media/v4l/controls.xml
> > >> @@ -3914,6 +3914,27 @@ by exposure, white balance or focus
> > >> controls.</entry>
> > >>           </row>
> > >>           <row><entry></entry></row>
> > >>
> > >> +         <row>
> > >> +           <entry
> > >> spanname="id"><constant>V4L2_CID_PAN_SPEED</constant>&nbsp;</entry>
> > >> +           <entry>integer</entry>
> > >> +         </row><row><entry spanname="descr">This control turns the
> > >> +camera horizontally at the specific speed. The unit is undefined. A
> > >> +positive value moves the camera to the right (clockwise when viewed
> > >> +from above), a negative value to the left. A value of zero does not
> > >> +cause or stop the motion.</entry>
> > >
> > >
> > > How do we stop/start?
> >
> > As mentioned in the last sentence of the paragraph above, setting 0
> > stops the movement.
> > setting non-zero value starts it if needed.
> >
>
> The sentence says "A value of zero does *not* cause or stop the
> motion.". Perhaps "not" is a typo then?


maybe my phrasing is really bad but the "not" isn't a typo.
The developed version would be :
"A value of zero does *not* cause [any motion if the camera is already stopped]
 or stop the motion [if it is currently moving with a non-zero speed]"

-- 
Vincent
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