From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Cochran Subject: Re: [PATCH net-next] dp83640: Adjust ptp event timestamps Date: Wed, 9 Jul 2014 19:41:49 +0200 Message-ID: <20140709174149.GA3859@localhost.localdomain> References: <1404901343-19445-1-git-send-email-stefan.sorensen@spectralink.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: netdev@vger.kernel.org To: Stefan =?iso-8859-1?Q?S=F8rensen?= Return-path: Received: from mail-wi0-f174.google.com ([209.85.212.174]:37700 "EHLO mail-wi0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755291AbaGIRmK (ORCPT ); Wed, 9 Jul 2014 13:42:10 -0400 Received: by mail-wi0-f174.google.com with SMTP id d1so902249wiv.13 for ; Wed, 09 Jul 2014 10:42:09 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1404901343-19445-1-git-send-email-stefan.sorensen@spectralink.com> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Jul 09, 2014 at 12:22:23PM +0200, Stefan S=F8rensen wrote: > From the dp86340 Software Development Guide: > Event timestamp values should be adjusted by 3*reference clock peri= od + > 11 ns =3D 35 ns to compensate for input path and synchronization de= lays. >=20 > So subtract 35ns from event timestamps. I have avoided adding this kind of thing into drivers because I think people will want to make the correction in the delayAsymmetry field of their user space stack. After all, this is exactly what that value is supposed to cover. Some parts have fixed delays (or at least they claim to) and some have variable delays that can depend on link speed or other factors. So my gut feeling tells me to be consistent and leave all such corrections out, because in that way the end user will not have to research whether a particular driver is "pre-correcting" or not. Thanks, Richard