From: Marc Zyngier <marc.zyngier@arm.com>
To: Vineet Gupta <Vineet.Gupta1@synopsys.com>,
Thomas Gleixner <tglx@linutronix.de>,
Jason Cooper <jason@lakedaemon.net>,
Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: linux-snps-arc@lists.infradead.org, linux-kernel@vger.kernel.org,
Noam Camus <noamc@ezchip.com>
Subject: Re: [PATCH v4 2/5] ARC: clocksource: DT based probe
Date: Thu, 14 Apr 2016 10:32:17 +0100 [thread overview]
Message-ID: <570F63A1.3070904@arm.com> (raw)
In-Reply-To: <570F623B.3000105@synopsys.com>
On 14/04/16 10:26, Vineet Gupta wrote:
> 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.
Unsynchronized counters on SMP HW, who would have thought! ;-) I guess
each and every architecture has to repeat the same mistakes.
Thanks for shedding some light on it.
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2016-04-14 9:32 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-13 11:40 [PATCH v4 0/5] Modernize ARC clocksource/clockevent/intc drivers Vineet Gupta
2016-04-13 11:40 ` [PATCH v4 1/5] ARC: clockevent: DT based probe Vineet Gupta
2016-04-13 12:59 ` Daniel Lezcano
2016-04-14 9:32 ` Vineet Gupta
2016-04-14 10:05 ` Daniel Lezcano
2016-04-18 6:46 ` [PATCH v5] " Vineet Gupta
2016-04-18 9:08 ` Daniel Lezcano
2016-04-13 11:40 ` [PATCH v4 2/5] ARC: clocksource: " Vineet Gupta
2016-04-13 16:22 ` Marc Zyngier
2016-04-14 9:26 ` Vineet Gupta
2016-04-14 9:32 ` Marc Zyngier [this message]
2016-04-14 9:36 ` Vineet Gupta
2016-04-13 11:40 ` [PATCH v4 3/5] ARC: irq: export some IRQs again Vineet Gupta
2016-04-13 11:40 ` [PATCH v4 4/5] ARC: [intc-*] Do a domain lookup in primary handler for hwirq -> linux virq Vineet Gupta
2016-04-13 11:40 ` [PATCH v4 5/5] ARC: [intc-*] switch to linear domain Vineet Gupta
2016-04-18 6:51 ` Vineet Gupta
2016-04-18 9:41 ` Marc Zyngier
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