From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756125AbYEODNI (ORCPT ); Wed, 14 May 2008 23:13:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752805AbYEODMz (ORCPT ); Wed, 14 May 2008 23:12:55 -0400 Received: from mail1.sea5.speakeasy.net ([69.17.117.3]:53392 "EHLO mail1.sea5.speakeasy.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752356AbYEODMz (ORCPT ); Wed, 14 May 2008 23:12:55 -0400 Date: Wed, 14 May 2008 20:12:53 -0700 (PDT) From: Trent Piepho X-X-Sender: xyzzy@shell4.speakeasy.net To: Greg KH cc: Markus Rechberger , video4linux-list@redhat.com, linux-usb@vger.kernel.org, dean@sensoray.com, linux-kernel@vger.kernel.org, mchehab@infradead.org, v4l-dvb-maintainer@linuxtv.org Subject: Re: [v4l-dvb-maintainer] [PATCH] USB: add Sensoray 2255 v4l driver In-Reply-To: <20080515024141.GB21941@kroah.com> Message-ID: References: <20080514205927.GA13134@kroah.com> <20080515024141.GB21941@kroah.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 14 May 2008, Greg KH wrote: > On Thu, May 15, 2008 at 03:17:42AM +0200, Markus Rechberger wrote: > > Hi Dean, Greg, > > Adding dean to the cc: line... :) > > > > On 5/14/08, Greg KH wrote: > > > From: Dean Anderson > > > > > > > > Why do you do those conversions in kernelspace? > > ffmpeg/libswscale has optimized code for colourspace conversions. > > I know a few drivers do that in kernelspace but it's way more flexible > > in userspace and depending on the optimization requires less CPU > > power. > > I thought they were there as needed by some V4L1 applications, but that > code was recently removed by Dean I think. If they don't need to be > there, and userspace apps can properly handle the different colorspace, > then I'll be glad to remove them. Virtually all apps (V4L1 & 2) can handle YUV and RGB colorspaces. Certainly all the major ones do and all the major libraries as well. The problem is when the device only supports some vendor specific or otherwise very uncommon format. In that case not doing the conversion in the kernel means the device won't work with any existing software without patches. In this case, while it's not "the right way", drivers often end up including an in kernel conversion for pragmatic reasons. This was a problem with the bayer format, but now userspace support for that format is more common.