Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753986Ab2H3RzE (ORCPT ); Thu, 30 Aug 2012 13:55:04 -0400 Received: from nblzone-211-213.nblnetworks.fi ([83.145.211.213]:36547 "EHLO hillosipuli.retiisi.org.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753617Ab2H3Ry4 (ORCPT ); Thu, 30 Aug 2012 13:54:56 -0400 Message-ID: <503FA8EC.8030309@iki.fi> Date: Thu, 30 Aug 2012 20:54:52 +0300 From: Sakari Ailus User-Agent: Mozilla/5.0 (X11; Linux i686; rv:14.0) Gecko/20120715 Firefox/14.0.1 SeaMonkey/2.11 MIME-Version: 1.0 To: Hans Verkuil CC: Prabhakar Lad , LMML , dlos , linux-kernel@vger.kernel.org, Manjunath Hadli , Hans Verkuil , Laurent Pinchart , Mauro Carvalho Chehab , Sylwester Nawrocki , Hans de Goede , Kyungmin Park Subject: Re: [PATCH v2] media: v4l2-ctrls: add control for dpcm predictor References: <1346313496-3652-1-git-send-email-prabhakar.lad@ti.com> <201208300757.44775.hverkuil@xs4all.nl> In-Reply-To: <201208300757.44775.hverkuil@xs4all.nl> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3929 Lines: 100 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 >> >> 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 >> Signed-off-by: Manjunath Hadli >> Cc: Sakari Ailus >> Cc: Hans Verkuil >> Cc: Laurent Pinchart >> Cc: Mauro Carvalho Chehab >> Cc: Sylwester Nawrocki >> Cc: Hans de Goede >> Cc: Kyungmin Park >> --- >> 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. >> pixels / second. >> >> >> - >> + >> + V4L2_CID_DPCM_PREDICTOR >> + menu >> + >> + >> + 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: 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/