From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754006AbbJNOXA (ORCPT ); Wed, 14 Oct 2015 10:23:00 -0400 Received: from www.linutronix.de ([62.245.132.108]:55463 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753917AbbJNOW6 (ORCPT ); Wed, 14 Oct 2015 10:22:58 -0400 Date: Wed, 14 Oct 2015 16:22:03 +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: <20151014092923.GA23870@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> <20151013211224.GA19242@netboy> <20151014092923.GA23870@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 Wed, 14 Oct 2015, Richard Cochran wrote: > On Wed, Oct 14, 2015 at 09:21:42AM +0200, Thomas Gleixner wrote: > > The firmware gives you an ART/audio timestamp pair. The firmware does > > neither know about system time nor about PTP time. > > > > So we have to do correlation in software. > > Ok, so give me the ART/audio and two recent ART/ptp times* spaced one > second apart, then I'll tell you audio/ptp with error well under 1 PPM. > No need to change the firmware. > > Who cares about the system time? If the DSP isn't using it, then just > leave it out of the equation. It's not only the DSP. There is a bunch of usre space software involved as well. Care to think about the full picture and not just about some randomly chosen single problem out of the full problem space. Thanks, tglx