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Date: Mon, 03 Sep 2012 11:21:12 +0200
From: Sylwester Nawrocki <s.nawrocki@...sung.com>
To: Prabhakar Lad <prabhakar.lad@...com>
Cc: 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, Sakari Ailus <sakari.ailus@....fi>,
Hans Verkuil <hans.verkuil@...co.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 v3] media: v4l2-ctrls: add control for dpcm predictor
On 09/03/2012 09:20 AM, Prabhakar Lad wrote:
> From: Lad, Prabhakar <prabhakar.lad@...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@...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>
> Cc: HeungJun Kim <riverful.kim@...sung.com>
Looks good.
Reviewed-by: Sylwester Nawrocki <s.nawrocki@...sung.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 v3:
> 1: Added better explanation for DPCM, pointed by Hans.
>
> 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 | 48 +++++++++++++++++++++++++-
> drivers/media/v4l2-core/v4l2-ctrls.c | 9 +++++
> include/linux/videodev2.h | 5 +++
> 3 files changed, 61 insertions(+), 1 deletions(-)
>
> diff --git a/Documentation/DocBook/media/v4l/controls.xml b/Documentation/DocBook/media/v4l/controls.xml
> index 93b9c68..f704218 100644
> --- a/Documentation/DocBook/media/v4l/controls.xml
> +++ b/Documentation/DocBook/media/v4l/controls.xml
> @@ -4267,7 +4267,53 @@ 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"> Differential pulse-code modulation (DPCM) is a signal
> + encoder that uses the baseline of pulse-code modulation (PCM) but adds some
> + functionalities based on the prediction of the samples of the signal. The input
> + can be an analog signal or a digital signal.
> +
> + <para>If the input is a continuous-time
> + analog signal, it needs to be sampled first so that a discrete-time signal is
> + the input to the DPCM encoder.</para>
nit: this whole paragraph could fit in 2 lines.
> +
> + <para>Simple: take the values of two
> + consecutive samples; if they are analog samples, quantize them; calculate the
> + difference between the first one and the next; the output is the difference, and
> + it can be further entropy coded.</para>
> +
> + <para>Advanced: instead of taking a difference relative to a previous input sample,
> + take the difference relative to the output of a local model of the decoder process;
> + in this option, the difference can be quantized, which allows a good way to
> + incorporate a controlled loss in the encoding.</para>
> +
> + <para>Applying one of these two processes, short-term redundancy (positive correlation of
> + nearby values) of the signal is eliminated; compression ratios on the order of 2 to 4
> + can be achieved if differences are subsequently entropy coded, because the entropy of
> + the difference signal is much smaller than that of the original discrete signal treated
> + as independent samples.For more information about DPCM see <ulink
> + url="http://en.wikipedia.org/wiki/Differential_pulse-code_modulation">Wikipedia</ulink>.</para>
> + </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
Regards,
Sylwester
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