From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <4C9BC7CE.8020400@riesch.at> Date: Thu, 23 Sep 2010 23:34:06 +0200 From: Christian Riesch MIME-Version: 1.0 To: Alan Cox Subject: Re: [PATCH v6 0/8] ptp: IEEE 1588 hardware clock support References: <1285268380.2587.11.camel@localhost.localdomain> <1285273684.2587.92.camel@localhost.localdomain> <20100923223417.4ed62e5b@lxorguk.ukuu.org.uk> In-Reply-To: <20100923223417.4ed62e5b@lxorguk.ukuu.org.uk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: Rodolfo Giometti , Arnd Bergmann , Peter Zijlstra , john stultz , devicetree-discuss@lists.ozlabs.org, linux-kernel@vger.kernel.org, David Miller , netdev@vger.kernel.org, Thomas Gleixner , linux-api@vger.kernel.org, Christoph Lameter , linuxppc-dev@lists.ozlabs.org, Richard Cochran , linux-arm-kernel@lists.infradead.org, Krzysztof Halasa List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Alan Cox wrote: >> It implies clock tuning in userspace for a potential sub microsecond >> accurate clock. The clock accuracy will be limited by user space >> latencies and noise. You wont be able to discipline the system clock >> accurately. > > Noise matters, latency doesn't. Well put! That's why we need hardware support for PTP timestamping to reduce the noise, but get along well with the clock servo that is steering the PHC in user space. Christian