From mboxrd@z Thu Jan 1 00:00:00 1970 From: Miroslav Lichvar Subject: Re: [PATCH RFC net-next 1/1] ptp: add an ioctl to compare PHC time with system time Date: Fri, 28 Sep 2012 09:53:03 +0200 Message-ID: <20120928075303.GB29438@localhost> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org, David Miller , Jacob Keller , John Stultz To: Richard Cochran Return-path: Received: from mx1.redhat.com ([209.132.183.28]:48097 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752619Ab2I1Hx6 (ORCPT ); Fri, 28 Sep 2012 03:53:58 -0400 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Thu, Sep 27, 2012 at 08:12:16PM +0200, Richard Cochran wrote: > This patch adds an ioctl for PTP Hardware Clock (PHC) devices that allows > user space to measure the time offset between the PHC and the system > clock. Rather than hard coding any kind of estimation algorithm into the > kernel, this patch takes the more flexible approach of just delivering > an array of raw clock readings. In that way, the user space clock servo > may be adapted to new and different hardware clocks. Would it make sense to extend the ioctl to allow also comparing the PHC with another PHC or perhaps even a different system clock than CLOCK_REALTIME? I'm thinking if someone wanted to synchronize one PHC to another, it should be better to work with phc1-phc2 offsets than combine phc1-sys and sys-phc2 offsets. -- Miroslav Lichvar