Messages in this thread | | | Date | Fri, 21 Jun 2013 10:12:37 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: clocksource with changing frequency? |
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On Thu, 20 Jun 2013, John Stultz wrote:
> On 06/20/2013 05:01 PM, Sören Brinkmann wrote: > > Hi all, > > > > I have a question/problem with a clocksource whose input frequency can > > change. > > That behavior isn't supported by the clocksource core. We expect frequency > changing clocksources to be detected and disqualified (as we do w/ freq > changing TSCs on older laptops). > > > > On Zynq we use the cadece_ttc timer as clocksource. Its input clock is > > tightly coupled to the CPU clock. I.e. it changes when cpufreq scales > > the CPU clocks. > > To compensate this, I added a clock notifier doing this on a frequency > > change: > > clocksource_unregister(&ttccs->cs); > > clocksource_register_hz(&ttccs->cs, ndata->new_rate / PRESCALE); > > This will definitely have problems if this is the only high-res capable > clocksource.
And starting with 3.11 it will be not longer possible to unregister the only high-res capable clocksource exactly to prevent the wreckage you are talking about :)
Thanks,
tglx
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