Re: [PATCH v4 2/5] ARC: clocksource: DT based probe

From	Vineet Gupta <Vineet.Gupta1@synopsys.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v4 2/5] ARC: clocksource: DT based probe
Date	2016-04-14 11:30 +0200
Message-ID	<rnLL5-7V2-29@gated-at.bofh.it> (permalink)
References	<rnrt0-BH-15@gated-at.bofh.it> <rnrt2-BH-71@gated-at.bofh.it> <rnvPY-3Yt-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Wednesday 13 April 2016 09:52 PM, Marc Zyngier wrote:
>> -int arc_counter_setup(void)
>> > +static void __init arc_cs_setup_rtc(struct device_node *node)
>> >  {
>> > -	write_aux_reg(ARC_REG_TIMER1_LIMIT, ARC_TIMER_MAX);
>> > -	write_aux_reg(ARC_REG_TIMER1_CNT, 0);
>> > -	write_aux_reg(ARC_REG_TIMER1_CTRL, TIMER_CTRL_NH);
>> > +	int exists = cpuinfo_arc700[smp_processor_id()].extn.rtc;
>> > +
>> > +	if (WARN(!exists, "Local-64-bit-Ctr clocksource not detected"))
>> > +		return;
>> > +
>> > +	/* Local to CPU hence not usable in SMP */
>> > +	if (WARN(IS_ENABLED(CONFIG_SMP), "Local-64-bit-Ctr not usable in SMP"))
>> > +		return;
> Sorry if this outlines my lack of understanding of the ARC architecture,
> but what makes per-cpu timer unsuitable for SMP? I'd have thought that
> it was actually what you wanted...

This is clocksource, not clockevent. cs needs to synchronized across all cores so
that concurrent gtod call from threads on different cores gives you similar
values. This obviously is not true for the local RTC hardware timer.

Thread

[PATCH v4 0/5] Modernize ARC clocksource/clockevent/intc drivers Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-04-13 13:50 +0200
  [PATCH v4 5/5] ARC: [intc-*] switch to linear domain Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-04-13 13:50 +0200
  [PATCH v4 3/5] ARC: irq: export some IRQs again Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-04-13 13:50 +0200
  [PATCH v4 4/5] ARC: [intc-*] Do a domain lookup in primary handler for hwirq -> linux virq Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-04-13 13:50 +0200
  [PATCH v4 1/5] ARC: clockevent: DT based probe Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-04-13 13:50 +0200
    Re: [PATCH v4 1/5] ARC: clockevent: DT based probe Daniel Lezcano <daniel.lezcano@linaro.org> - 2016-04-13 15:00 +0200
      Re: [PATCH v4 1/5] ARC: clockevent: DT based probe Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-04-14 11:40 +0200
        Re: [PATCH v4 1/5] ARC: clockevent: DT based probe Daniel Lezcano <daniel.lezcano@linaro.org> - 2016-04-14 12:10 +0200
  [PATCH v4 2/5] ARC: clocksource: DT based probe Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-04-13 13:50 +0200
    Re: [PATCH v4 2/5] ARC: clocksource: DT based probe Marc Zyngier <marc.zyngier@arm.com> - 2016-04-13 18:30 +0200
      Re: [PATCH v4 2/5] ARC: clocksource: DT based probe Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-04-14 11:30 +0200
        Re: [PATCH v4 2/5] ARC: clocksource: DT based probe Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-04-14 11:40 +0200
        Re: [PATCH v4 2/5] ARC: clocksource: DT based probe Marc Zyngier <marc.zyngier@arm.com> - 2016-04-14 11:40 +0200

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