linux-kernel - Re: [PATCH v2] media: v4l2-ctrls: add control for test pattern

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Date:	Sat, 8 Sep 2012 13:11:04 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Sakari Ailus <sakari.ailus@....fi>
Cc:	Prabhakar Lad <prabhakar.lad@...com>,
	LMML <linux-media@...r.kernel.org>,
	dlos <davinci-linux-open-source@...ux.davincidsp.com>,
	linux-kernel@...r.kernel.org,
	Manjunath Hadli <manjunath.hadli@...com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	linux-doc@...r.kernel.org, Hans Verkuil <hans.verkuil@...co.com>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Hans de Goede <hdegoede@...hat.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Rob Landley <rob@...dley.net>
Subject: Re: [PATCH v2] media: v4l2-ctrls: add control for test pattern

On Fri September 7 2012 20:20:51 Sakari Ailus wrote:
> Hi Prabhakar,
> 
> Thanks for the patch!
> 
> Prabhakar Lad wrote:
> > From: Lad, Prabhakar <prabhakar.lad@...com>
> >
> > add V4L2_CID_TEST_PATTERN of type menu, which determines
> > the internal test pattern selected by the device.
> >
> > Signed-off-by: Lad, Prabhakar <prabhakar.lad@...com>
> > Signed-off-by: Manjunath Hadli <manjunath.hadli@...com>
> > Cc: Sakari Ailus <sakari.ailus@....fi>
> > Cc: Hans Verkuil <hans.verkuil@...co.com>
> > Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > Cc: Mauro Carvalho Chehab <mchehab@...radead.org>
> > Cc: Sylwester Nawrocki <s.nawrocki@...sung.com>
> > Cc: Hans de Goede <hdegoede@...hat.com>
> > Cc: Kyungmin Park <kyungmin.park@...sung.com>
> > Cc: Rob Landley <rob@...dley.net>
> > ---
> > This patches has one checkpatch warning for line over
> > 80 characters altough it can be avoided I have kept it
> > for consistency.
> >
> > Changes for v2:
> > 1: Included display devices in the description for test pattern
> >     as pointed by Hans.
> > 2: In the menu replaced 'Test Pattern Disabled' by 'Disabled' as
> >     pointed by Sylwester.
> > 3: Removed the test patterns from menu as the are hardware specific
> >     as pointed by Sakari.
> >
> >   Documentation/DocBook/media/v4l/controls.xml |   20 ++++++++++++++++++++
> >   drivers/media/v4l2-core/v4l2-ctrls.c         |    8 ++++++++
> >   include/linux/videodev2.h                    |    4 ++++
> >   3 files changed, 32 insertions(+), 0 deletions(-)
> >
> > diff --git a/Documentation/DocBook/media/v4l/controls.xml b/Documentation/DocBook/media/v4l/controls.xml
> > index ad873ea..173934e 100644
> > --- a/Documentation/DocBook/media/v4l/controls.xml
> > +++ b/Documentation/DocBook/media/v4l/controls.xml
> > @@ -4311,6 +4311,26 @@ interface and may change in the future.</para>
> >   	      </tbody>
> >   	    </entrytbl>
> >   	  </row>
> > +	  <row>
> > +	    <entry spanname="id"><constant>V4L2_CID_TEST_PATTERN</constant></entry>
> > +	    <entry>menu</entry>
> > +	  </row>
> > +	  <row id="v4l2-test-pattern">
> > +	    <entry spanname="descr"> The Capture/Display/Sensors have the capability
> > +	    to generate internal test patterns and this are hardware specific. This
> > +	    test patterns are used to test a device is properly working and can generate
> > +	    the desired waveforms that it supports.</entry>
> > +	  </row>
> > +	  <row>
> > +	    <entrytbl spanname="descr" cols="2">
> > +	      <tbody valign="top">
> > +	        <row>
> > +	         <entry><constant>V4L2_TEST_PATTERN_DISABLED</constant></entry>
> > +	          <entry>Test pattern generation is disabled</entry>
> > +	        </row>
> > +	      </tbody>
> > +	    </entrytbl>
> > +	  </row>
> >   	<row><entry></entry></row>
> >   	</tbody>
> >         </tgroup>
> > diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> > index 8f2f40b..d731422 100644
> > --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> > +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> > @@ -430,6 +430,10 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
> >   		"Advanced",
> >   		NULL,
> >   	};
> > +	static const char * const test_pattern[] = {
> > +		"Disabled",
> > +		NULL,
> > +	};
> >
> >   	switch (id) {
> >   	case V4L2_CID_MPEG_AUDIO_SAMPLING_FREQ:
> > @@ -509,6 +513,8 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
> >   		return jpeg_chroma_subsampling;
> >   	case V4L2_CID_DPCM_PREDICTOR:
> >   		return dpcm_predictor;
> > +	case V4L2_CID_TEST_PATTERN:
> > +		return test_pattern;
> 
> I think it's not necessary to define test_pattern (nor be prepared to 
> return it) since the menu is going to be device specific. So the driver 
> is responsible for all of the menu items. Such menus are created using 
> v4l2_ctrl_new_custom() instead of v4l2_ctrl_new_std_menu().
> 
> Looks good to me otherwise.

I would suggest that we *do* make this a standard control, but the menu consists
of just one item: "Disabled". After creating the control you can just set the
ctrl->qmenu pointer to the device-specific menu. I like using standard controls
because they guarantee standard naming and type conventions. They are also
easier to use in an application.

This would obvious require good documentation, both in the code and in the
spec.

BTW, see also this patch that needs to use the test pattern control:

http://www.spinics.net/lists/linux-media/msg52747.html

Regards,

	Hans
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