From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752184AbbJMTQr (ORCPT ); Tue, 13 Oct 2015 15:16:47 -0400 Received: from www.linutronix.de ([62.245.132.108]:51876 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750752AbbJMTQq (ORCPT ); Tue, 13 Oct 2015 15:16:46 -0400 Date: Tue, 13 Oct 2015 21:15:51 +0200 (CEST) From: Thomas Gleixner To: Richard Cochran cc: "Christopher S. Hall" , jeffrey.t.kirsher@intel.com, hpa@zytor.com, mingo@redhat.com, john.stultz@linaro.org, peterz@infradead.org, x86@kernel.org, intel-wired-lan@lists.osuosl.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kevin.b.stanton@intel.com Subject: Re: [PATCH v4 1/4] Produce system time from correlated clocksource In-Reply-To: <20151013083113.GA1931@localhost.localdomain> Message-ID: References: <1444675522-4198-1-git-send-email-christopher.s.hall@intel.com> <1444675522-4198-2-git-send-email-christopher.s.hall@intel.com> <20151013045832.GA2437@netboy> <20151013083113.GA1931@localhost.localdomain> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 13 Oct 2015, Richard Cochran wrote: > On Tue, Oct 13, 2015 at 09:51:02AM +0200, Thomas Gleixner wrote: > > > > You are restricting the problem space to this particular use > > case. There are other use cases where PTP is not available or not the > > relevant reference, but you still want to correlate time domains to > > ART. > > They may well be other use cases, but they have not been identified > here. The PTP to media clock problem has a very simple solution. You > do not need a history of system time stamps to solve it. Well, these use cases are not in the focus of Christopher, but I have a few in my head. Think industrial fieldbusses. > Even if you wanted to correlate the system time's UTC with the media > clock, still you don't need any shadow history for that. Just feed > (ART, UTC) pairs into the DSP at a regular rate, and let the DSP do > the math. This does not need to be part of the central time keeping > code at all. That's not working. The firmware is not going to change, no matter what. Thanks, tglx