From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Cochran Subject: Re: [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks. Date: Mon, 16 Aug 2010 21:00:03 +0200 Message-ID: <20100816190003.GB4166@riccoc20.at.omicron.at> References: <363bd749a38d0b785d8431e591bf54c38db4c2d7.1281956490.git.richard.cochran@omicron.at> <201008161626.24083.arnd@arndb.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <201008161626.24083.arnd@arndb.de> Sender: netdev-owner@vger.kernel.org To: Arnd Bergmann Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, devicetree-discuss@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, Krzysztof Halasa , Rodolfo Giometti List-Id: devicetree@vger.kernel.org On Mon, Aug 16, 2010 at 04:26:23PM +0200, Arnd Bergmann wrote: > Have you considered integrating the subsystem into the Posix clock/timer > framework? Yes, but see below. > I can't really tell from reading the source if this is possible or > not, but my feeling is that if it can be done, that would be a much > nicer interface. We already have clock_gettime/clock_settime/ > timer_settime/... system calls, and while you'd need to add another > clockid and some syscalls, my feeling is that it will be more > usable in the end. You are not the first person to ask about this. See this link for longer explanation of why I did not go that way: http://marc.info/?l=linux-netdev&m=127669810232201&w=2 You *could* offer the PTP clock as a Linux clock source/event device, and I agree that it would be nicer. However, the problem is, what do you do with the PHY based clocks? Just one 16 bit read from a PHY clock can take 40 usec, and you need four such read operations just to get the current time value. Also, I really did not want to add or change any syscalls. I could not see a practical way to extend the existing syscalls to accommodate PTP clocks. Richard