From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-bk0-f46.google.com ([209.85.214.46]:35282 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1768414Ab2KOQ6i (ORCPT ); Thu, 15 Nov 2012 11:58:38 -0500 Received: by mail-bk0-f46.google.com with SMTP id q16so829916bkw.19 for ; Thu, 15 Nov 2012 08:58:36 -0800 (PST) Message-ID: <50A51F3B.9050400@googlemail.com> Date: Thu, 15 Nov 2012 17:58:35 +0100 From: =?ISO-8859-1?Q?Frank_Sch=E4fer?= MIME-Version: 1.0 To: Devin Heitmueller CC: Michael Yang , linux-media@vger.kernel.org, Mauro Carvalho Chehab Subject: Re: The em28xx driver error References: <50A3CDCD.6020900@googlemail.com> <50A518E8.8060002@googlemail.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-media-owner@vger.kernel.org List-ID: Am 15.11.2012 17:35, schrieb Devin Heitmueller: > On Thu, Nov 15, 2012 at 11:31 AM, Frank Schäfer > wrote: >> Hmm... I've made some experiments to find out what gcc does on x86 and >> it seems to ignore bit shifting > 32. >> I also noticed that this line has been removed in 3.7-rc. >> So we do NOT want to halve the height for interlaced devices here, right ? > Even with the datasheets, it was never clear to me what role the > accumulator size played. It appeared to work regardless of whether it > was halved (although making it zero obviously caused problems). > > Hence, since we couldn't see any visible difference, Mauro just > removed the code. My guess is that it effects the on-chip internal > buffering hence it's possible that performance/reliability could be > effected under extreme load or some edge case, but I don't have any > data to back up that assertion at this time. > > Devin > Interesting. As the buggy line seemed to have no effect on x86 and the driver was working fine, it makes indeed sense to stay with the full height to avoid regressions. Regards, Frank