From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Cochran Subject: Re: [PATCH] Add PTP cross-timestamp to the PTP driver interface Date: Fri, 26 Jun 2015 08:55:07 +0200 Message-ID: <20150626065507.GB1511@localhost.localdomain> References: <1435275777-3918-1-git-send-email-christopher.s.hall@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org, jacob.e.keller@intel.com, john.ronciak@intel.com, kevin.b.stanton@intel.com To: Christopher Hall Return-path: Received: from mail-wi0-f169.google.com ([209.85.212.169]:34452 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752034AbbFZGzM (ORCPT ); Fri, 26 Jun 2015 02:55:12 -0400 Received: by wicnd19 with SMTP id nd19so36703724wic.1 for ; Thu, 25 Jun 2015 23:55:11 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1435275777-3918-1-git-send-email-christopher.s.hall@intel.com> Sender: netdev-owner@vger.kernel.org List-ID: Chris, Basically this patch looks okay to me. Could you please add LKML, John Stultz and tglx (the time guys) onto CC? I would like to get their Acks or at least let them have a chance to review it. On Thu, Jun 25, 2015 at 04:42:56PM -0700, Christopher Hall wrote: > This patch allows system and device time ("cross-timestamp") to be performed > by the driver. Currently, the timestamping is performed in the PTP_SYS_OFFSET > ioctl. It reads gettimeofday() and the gettime64() callback provided by the > driver. The cross-timestamp is best effort ignoring the latency between the > capture of system time (getnstimeofday()) and the device time > (driver callback). You can make the motivation more clear by mentioning how the newer PCIe spec foresees "perfect" timestamps. If I didn't already know the background, I would wonder who would ever want "best effort" single cross timestamps. > Additionally, the callback, getsynctime64(), will only be called when > n_samples == 1 because the driver returns only 1 cross-timestamp where > multiple samples cannot be chained together. There should be a way for user space to find out whether a particular device offers the cross timestamp capability. There are reserved fields in 'struct ptp_clock_caps' that could be used. Thanks, Richard