From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Cochran Subject: Re: [PATCH 04/12] phylib: add a way to make PHY time stamps possible. Date: Wed, 16 Jun 2010 07:40:47 +0200 Message-ID: <20100616054047.GA2887@riccoc20.at.omicron.at> References: <27c0ad283f025c2bb71e7ceb71be07f969939429.1276615626.git.richard.cochran@omicron.at> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org To: Grant Likely Cc: netdev@vger.kernel.org, devicetree-discuss@lists.ozlabs.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, Krzysztof Halasa List-Id: devicetree@vger.kernel.org On Tue, Jun 15, 2010 at 10:33:51AM -0600, Grant Likely wrote: > > +config NETWORK_PHY_TIMESTAMPING > Some overhead? At a brief glance of the series it looks like it could > add a lot of overhead, but I'm not fully clear on what the full > process is. Can you describe how the hardware timestamping works? I > could use an overview of what the kernel has to do. First of all, I want to emphasize that this network stack option is purely voluntary. Only those people who know that they have a PTP capable PHY and really want the timestamps will (or should) enable this option. When it is not enabled, it has no effect at all. Hardware timestamping is described in Documentation/networking/timestamping.txt Documentation/networking/timestamping/timestamping.c The PTP subsystem is described in Documentation/ptp/ptp.txt There really is more to say about the issue than appears in those documents, but they are a good starting place for discussion. BTW I am submitting a conference paper on the design on the PTP subsystem. If you would like to have it, just ask me off-list. Richard