Messages in this thread | | | Date | Tue, 13 Apr 2010 07:44:35 +0200 | From | Giuseppe CAVALLARO <> | Subject | Re: re-adding clocksource_get_next ? |
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On 04/12/2010 08:50 PM, john stultz wrote: > On Mon, 2010-04-12 at 08:02 +0200, Giuseppe CAVALLARO wrote: >> -----BEGIN PGP SIGNED MESSAGE----- >> Hash: SHA1 >> >> Hello John, >> >> john stultz wrote: >>> On Thu, Apr 8, 2010 at 11:53 PM, Giuseppe CAVALLARO >>> <peppe.cavallaro@st.com> wrote: >>>> Hello! >>>> this function was removed in the past but I've not clear all the details. >>>> While testing LLTng, I wrote the patch, in attachment, that re-adds it >>>> again. >>>> The clocksource_get_next returns the first clock source available >>>> (without looking at the rating). >>>> In my environment, a clock source is a TMU channel (e.g. TMU1) and, >>>> indeed, clocksource_get_next works fine. >>> >>> Could you provide some more details as to why you need raw access to >>> the clocksource, instead of using something like ktime_get(), >>> getrawmonotonic() or sched_clock()? >> >> I wanted to directly read the value of the TCNT register of a TMU >> channel registered as clocksource in an SH platform. >> My idea was to get the first clocksource available and than use the read >> hook to get its raw value. >> Indeed, on SH4, the clocksource_get_next returns the TMU channel 1 >> (usually registered as clocksource); the clk->reads points to >> sh_tmu_clocksource_read (drivers/clocksource/sh_tmu.c). This returns the >> value of the timer count register (TCNT). > > If you specifically want the function sh_tmu_clocksource_read(), why not > call it directly instead of indirecting through the clocksource > infrastructure? > > Additionally, since the clocksource code is dynamic, you might get a > different clocksource then you expect (such as jiffies) depending on > user config or user actions. > > So I'd advise against using the clocksource code here.
This means I should export the sh_tmu_clocksource_read (currently static) and don't pass for the clocksource code at all.
Thanks for your prompt feedback.
Best Regards, Giuseppe
> thanks > -john -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/
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