[PATCH v2] media: v4l2-ctrls: add control for dpcm predictor

[PATCH v2] media: v4l2-ctrls: add control for dpcm predictor

[Prabhakar Lad]

From: Lad, Prabhakar <prabhakar.lad@ti.com>

add V4L2_CID_DPCM_PREDICTOR control of type menu, which
determines the dpcm predictor. The predictor can be either
simple or advanced.

Signed-off-by: Lad, Prabhakar <prabhakar.lad@ti.com>
Signed-off-by: Manjunath Hadli <manjunath.hadli@ti.com>
Cc: Sakari Ailus <sakari.ailus@iki.fi>
Cc: Hans Verkuil <hans.verkuil@cisco.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
---
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: Added documentaion in controls.xml pointed by Sylwester.
2: Chnaged V4L2_DPCM_PREDICTOR_ADVANCE to V4L2_DPCM_PREDICTOR_ADVANCED
   pointed by Sakari.

 Documentation/DocBook/media/v4l/controls.xml |   25 ++++++++++++++++++++++++-
 drivers/media/v4l2-core/v4l2-ctrls.c         |    9 +++++++++
 include/linux/videodev2.h                    |    5 +++++
 3 files changed, 38 insertions(+), 1 deletions(-)

diff --git a/Documentation/DocBook/media/v4l/controls.xml b/Documentation/DocBook/media/v4l/controls.xml
index 93b9c68..84746d0 100644
--- a/Documentation/DocBook/media/v4l/controls.xml
+++ b/Documentation/DocBook/media/v4l/controls.xml
@@ -4267,7 +4267,30 @@ interface and may change in the future.</para>
 	    pixels / second.
 	    </entry>
 	  </row>
-	  <row><entry></entry></row>
+	  <row>
+	    <entry spanname="id"><constant>V4L2_CID_DPCM_PREDICTOR</constant></entry>
+	    <entry>menu</entry>
+	  </row>
+	  <row id="v4l2-dpcm-predictor">
+	    <entry spanname="descr"> DPCM Predictor: depicts what type of prediction
+	    is used simple or advanced.
+	    </entry>
+	  </row>
+	  <row>
+	    <entrytbl spanname="descr" cols="2">
+	      <tbody valign="top">
+	        <row>
+	         <entry><constant>V4L2_DPCM_PREDICTOR_SIMPLE</constant></entry>
+	          <entry>Predictor type is simple</entry>
+	        </row>
+	        <row>
+	          <entry><constant>V4L2_DPCM_PREDICTOR_ADVANCED</constant></entry>
+	          <entry>Predictor type is advanced</entry>
+	        </row>
+	      </tbody>
+	    </entrytbl>
+	  </row>
+	<row><entry></entry></row>
 	</tbody>
       </tgroup>
       </table>
diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
index b6a2ee7..2d7bc15 100644
--- a/drivers/media/v4l2-core/v4l2-ctrls.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls.c
@@ -425,6 +425,11 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
 		"Gray",
 		NULL,
 	};
+	static const char * const dpcm_predictor[] = {
+		"Simple Predictor",
+		"Advanced Predictor",
+		NULL,
+	};
 
 	switch (id) {
 	case V4L2_CID_MPEG_AUDIO_SAMPLING_FREQ:
@@ -502,6 +507,8 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
 		return mpeg4_profile;
 	case V4L2_CID_JPEG_CHROMA_SUBSAMPLING:
 		return jpeg_chroma_subsampling;
+	case V4L2_CID_DPCM_PREDICTOR:
+		return dpcm_predictor;
 
 	default:
 		return NULL;
@@ -732,6 +739,7 @@ const char *v4l2_ctrl_get_name(u32 id)
 	case V4L2_CID_IMAGE_PROC_CLASS:		return "Image Processing Controls";
 	case V4L2_CID_LINK_FREQ:		return "Link Frequency";
 	case V4L2_CID_PIXEL_RATE:		return "Pixel Rate";
+	case V4L2_CID_DPCM_PREDICTOR:		return "DPCM Predictor";
 
 	default:
 		return NULL;
@@ -832,6 +840,7 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
 	case V4L2_CID_ISO_SENSITIVITY_AUTO:
 	case V4L2_CID_EXPOSURE_METERING:
 	case V4L2_CID_SCENE_MODE:
+	case V4L2_CID_DPCM_PREDICTOR:
 		*type = V4L2_CTRL_TYPE_MENU;
 		break;
 	case V4L2_CID_LINK_FREQ:
diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
index 6d6dfa7..ca9fb78 100644
--- a/include/linux/videodev2.h
+++ b/include/linux/videodev2.h
@@ -2000,6 +2000,11 @@ enum v4l2_jpeg_chroma_subsampling {
 
 #define V4L2_CID_LINK_FREQ			(V4L2_CID_IMAGE_PROC_CLASS_BASE + 1)
 #define V4L2_CID_PIXEL_RATE			(V4L2_CID_IMAGE_PROC_CLASS_BASE + 2)
+#define V4L2_CID_DPCM_PREDICTOR			(V4L2_CID_IMAGE_PROC_CLASS_BASE + 3)
+enum v4l2_dpcm_predictor {
+	V4L2_DPCM_PREDICTOR_SIMPLE	= 0,
+	V4L2_DPCM_PREDICTOR_ADVANCED	= 1,
+};
 
 /*
  *	T U N I N G
-- 
1.7.0.4

Re: [PATCH v2] media: v4l2-ctrls: add control for dpcm predictor

[Hans Verkuil]

Hi Prabhakar!

I've got some documentation review comments below...

On Thu August 30 2012 00:58:16 Prabhakar Lad wrote:
> From: Lad, Prabhakar <prabhakar.lad@ti.com>
> 
> add V4L2_CID_DPCM_PREDICTOR control of type menu, which
> determines the dpcm predictor. The predictor can be either
> simple or advanced.
> 
> Signed-off-by: Lad, Prabhakar <prabhakar.lad@ti.com>
> Signed-off-by: Manjunath Hadli <manjunath.hadli@ti.com>
> Cc: Sakari Ailus <sakari.ailus@iki.fi>
> Cc: Hans Verkuil <hans.verkuil@cisco.com>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
> Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>
> Cc: Hans de Goede <hdegoede@redhat.com>
> Cc: Kyungmin Park <kyungmin.park@samsung.com>
> ---
> 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: Added documentaion in controls.xml pointed by Sylwester.
> 2: Chnaged V4L2_DPCM_PREDICTOR_ADVANCE to V4L2_DPCM_PREDICTOR_ADVANCED
>    pointed by Sakari.
> 
>  Documentation/DocBook/media/v4l/controls.xml |   25 ++++++++++++++++++++++++-
>  drivers/media/v4l2-core/v4l2-ctrls.c         |    9 +++++++++
>  include/linux/videodev2.h                    |    5 +++++
>  3 files changed, 38 insertions(+), 1 deletions(-)
> 
> diff --git a/Documentation/DocBook/media/v4l/controls.xml b/Documentation/DocBook/media/v4l/controls.xml
> index 93b9c68..84746d0 100644
> --- a/Documentation/DocBook/media/v4l/controls.xml
> +++ b/Documentation/DocBook/media/v4l/controls.xml
> @@ -4267,7 +4267,30 @@ interface and may change in the future.</para>
>  	    pixels / second.
>  	    </entry>
>  	  </row>
> -	  <row><entry></entry></row>
> +	  <row>
> +	    <entry spanname="id"><constant>V4L2_CID_DPCM_PREDICTOR</constant></entry>
> +	    <entry>menu</entry>
> +	  </row>
> +	  <row id="v4l2-dpcm-predictor">
> +	    <entry spanname="descr"> DPCM Predictor: depicts what type of prediction
> +	    is used simple or advanced.

This is not useful information. It basically just rephrases the name of the
define without actually telling me anything.

I would expect to see here at least the following:

- what the DPCM abbreviation stands for
- a link or bibliography reference to the relevant standard (if there is any)
- a high-level explanation of what this do and what the difference is between
 simple and advanced.

If this is part of a video compression standard, then this control would probably
belong to the MPEG control class as well.

Regards,

    Hans


> +	    </entry>
> +	  </row>
> +	  <row>
> +	    <entrytbl spanname="descr" cols="2">
> +	      <tbody valign="top">
> +	        <row>
> +	         <entry><constant>V4L2_DPCM_PREDICTOR_SIMPLE</constant></entry>
> +	          <entry>Predictor type is simple</entry>
> +	        </row>
> +	        <row>
> +	          <entry><constant>V4L2_DPCM_PREDICTOR_ADVANCED</constant></entry>
> +	          <entry>Predictor type is advanced</entry>
> +	        </row>
> +	      </tbody>
> +	    </entrytbl>
> +	  </row>
> +	<row><entry></entry></row>
>  	</tbody>
>        </tgroup>
>        </table>
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> index b6a2ee7..2d7bc15 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> @@ -425,6 +425,11 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
>  		"Gray",
>  		NULL,
>  	};
> +	static const char * const dpcm_predictor[] = {
> +		"Simple Predictor",
> +		"Advanced Predictor",
> +		NULL,
> +	};
>  
>  	switch (id) {
>  	case V4L2_CID_MPEG_AUDIO_SAMPLING_FREQ:
> @@ -502,6 +507,8 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
>  		return mpeg4_profile;
>  	case V4L2_CID_JPEG_CHROMA_SUBSAMPLING:
>  		return jpeg_chroma_subsampling;
> +	case V4L2_CID_DPCM_PREDICTOR:
> +		return dpcm_predictor;
>  
>  	default:
>  		return NULL;
> @@ -732,6 +739,7 @@ const char *v4l2_ctrl_get_name(u32 id)
>  	case V4L2_CID_IMAGE_PROC_CLASS:		return "Image Processing Controls";
>  	case V4L2_CID_LINK_FREQ:		return "Link Frequency";
>  	case V4L2_CID_PIXEL_RATE:		return "Pixel Rate";
> +	case V4L2_CID_DPCM_PREDICTOR:		return "DPCM Predictor";
>  
>  	default:
>  		return NULL;
> @@ -832,6 +840,7 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
>  	case V4L2_CID_ISO_SENSITIVITY_AUTO:
>  	case V4L2_CID_EXPOSURE_METERING:
>  	case V4L2_CID_SCENE_MODE:
> +	case V4L2_CID_DPCM_PREDICTOR:
>  		*type = V4L2_CTRL_TYPE_MENU;
>  		break;
>  	case V4L2_CID_LINK_FREQ:
> diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
> index 6d6dfa7..ca9fb78 100644
> --- a/include/linux/videodev2.h
> +++ b/include/linux/videodev2.h
> @@ -2000,6 +2000,11 @@ enum v4l2_jpeg_chroma_subsampling {
>  
>  #define V4L2_CID_LINK_FREQ			(V4L2_CID_IMAGE_PROC_CLASS_BASE + 1)
>  #define V4L2_CID_PIXEL_RATE			(V4L2_CID_IMAGE_PROC_CLASS_BASE + 2)
> +#define V4L2_CID_DPCM_PREDICTOR			(V4L2_CID_IMAGE_PROC_CLASS_BASE + 3)
> +enum v4l2_dpcm_predictor {
> +	V4L2_DPCM_PREDICTOR_SIMPLE	= 0,
> +	V4L2_DPCM_PREDICTOR_ADVANCED	= 1,
> +};
>  
>  /*
>   *	T U N I N G
> 

Re: [PATCH v2] media: v4l2-ctrls: add control for dpcm predictor

[Sakari Ailus]

Hi Hans and Prabhakar,

Hans Verkuil wrote:
> Hi Prabhakar!
>
> I've got some documentation review comments below...
>
> On Thu August 30 2012 00:58:16 Prabhakar Lad wrote:
>> From: Lad, Prabhakar <prabhakar.lad@ti.com>
>>
>> add V4L2_CID_DPCM_PREDICTOR control of type menu, which
>> determines the dpcm predictor. The predictor can be either
>> simple or advanced.
>>
>> Signed-off-by: Lad, Prabhakar <prabhakar.lad@ti.com>
>> Signed-off-by: Manjunath Hadli <manjunath.hadli@ti.com>
>> Cc: Sakari Ailus <sakari.ailus@iki.fi>
>> Cc: Hans Verkuil <hans.verkuil@cisco.com>
>> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>> Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
>> Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>
>> Cc: Hans de Goede <hdegoede@redhat.com>
>> Cc: Kyungmin Park <kyungmin.park@samsung.com>
>> ---
>> 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: Added documentaion in controls.xml pointed by Sylwester.
>> 2: Chnaged V4L2_DPCM_PREDICTOR_ADVANCE to V4L2_DPCM_PREDICTOR_ADVANCED
>>     pointed by Sakari.
>>
>>   Documentation/DocBook/media/v4l/controls.xml |   25 ++++++++++++++++++++++++-
>>   drivers/media/v4l2-core/v4l2-ctrls.c         |    9 +++++++++
>>   include/linux/videodev2.h                    |    5 +++++
>>   3 files changed, 38 insertions(+), 1 deletions(-)
>>
>> diff --git a/Documentation/DocBook/media/v4l/controls.xml b/Documentation/DocBook/media/v4l/controls.xml
>> index 93b9c68..84746d0 100644
>> --- a/Documentation/DocBook/media/v4l/controls.xml
>> +++ b/Documentation/DocBook/media/v4l/controls.xml
>> @@ -4267,7 +4267,30 @@ interface and may change in the future.</para>
>>   	    pixels / second.
>>   	    </entry>
>>   	  </row>
>> -	  <row><entry></entry></row>
>> +	  <row>
>> +	    <entry spanname="id"><constant>V4L2_CID_DPCM_PREDICTOR</constant></entry>
>> +	    <entry>menu</entry>
>> +	  </row>
>> +	  <row id="v4l2-dpcm-predictor">
>> +	    <entry spanname="descr"> DPCM Predictor: depicts what type of prediction
>> +	    is used simple or advanced.
>
> This is not useful information. It basically just rephrases the name of the
> define without actually telling me anything.
>
> I would expect to see here at least the following:
>
> - what the DPCM abbreviation stands for
> - a link or bibliography reference to the relevant standard (if there is any)

There's a Wikipedia article:

<URL:http://en.wikipedia.org/wiki/Differential_pulse-code_modulation>

It's the same DPCM encoding as in many of the compressed raw bayer formats.

> - a high-level explanation of what this do and what the difference is between
>   simple and advanced.

That's somewhat subjective and hardware dependent. If I understand this 
correctly, the "advanced" should differ only quality-wise from "simple" 
option. Why one would use "simple" instead of "advanced" then? Perhaps 
mostly for testing purposes; it might be that the advanced predictor 
could have issues in certain cases where the simple would not. However 
this isn't the only piece of hardware where I see that this is 
configurable, and the simple one was even the default.

> If this is part of a video compression standard, then this control would probably
> belong to the MPEG control class as well.

It's not --- DPCM compression is typically used on the bus between the 
sensor and the receiver to compress the data as the bus is often a 
limiting factor in the transfer rate. DPCM compression can be used to 
squeeze the data from 10 to 8 bits without much loss in quality or 
dynamic range.

Cheers,

-- 
Sakari Ailus
sakari.ailus@iki.fi