From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gateway-1237.mvista.com (gateway-1237.mvista.com [63.81.120.158]) by ozlabs.org (Postfix) with ESMTP id DD167DDE33 for ; Sun, 20 May 2007 12:45:37 +1000 (EST) Subject: Re: [PATCH 2.6.21-rt2] PowerPC: decrementer clockevent driver From: Daniel Walker To: Paul Mackerras In-Reply-To: <17998.28659.702653.237011@cargo.ozlabs.ibm.com> References: <200705172142.26739.sshtylyov@ru.mvista.com> <8E44DB06-767D-4864-8D2C-6132E4D4370B@kernel.crashing.org> <464C99FF.8080404@ru.mvista.com> <135307ED-7125-4859-8594-4B5B900D92D6@kernel.crashing.org> <1179500217.20519.53.camel@imap.mvista.com> <464DC0DC.7050809@ru.mvista.com> <1179502773.20519.56.camel@imap.mvista.com> <17998.28659.702653.237011@cargo.ozlabs.ibm.com> Content-Type: text/plain Date: Sat, 19 May 2007 19:43:11 -0700 Message-Id: <1179628991.20925.2.camel@imap.mvista.com> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org, tglx@linutronix.de, mingo@elte.hu, linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, 2007-05-19 at 13:33 +1000, Paul Mackerras wrote: > Daniel Walker writes: > > > On Fri, 2007-05-18 at 19:06 +0400, Sergei Shtylyov wrote: > > > Well, the decrementer frequency may change, at least in theory (if the bus > > > clock changes). > > > > Does that happen very often? > > If it did, gettimeofday would start reporting seriously wrong values, > since the timebase and the decrementer count at the same rate, and we > don't have any provision for fixing things up if that rate changed. > Fortunately there are no powerpc platforms where the rate is > variable. In terms of clocksources, gettimeofday() would have to switch to another clocksource if the decrementer started to act that way .. That's why it is possible to register more than one clocksource, to allow for the switching. The decrementer frequency doesn't change even with cpufreq? Daniel