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

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Message-ID: <570F648A.2060307@synopsys.com>
Date:	Thu, 14 Apr 2016 15:06:10 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Marc Zyngier <marc.zyngier@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
CC:	<linux-snps-arc@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, Noam Camus <noamc@...hip.com>
Subject: Re: [PATCH v4 2/5] ARC: clocksource: DT based probe

On Thursday 14 April 2016 03:02 PM, Marc Zyngier wrote:
>> 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.

Not really - hardware wise the SMP support is pretty recent and before that we
only had UP cores. So transition from 32 TIMER1 to 64 bit RTC was only a natural
progression in improvements and in theory SoC guys throw in this local timer into
the config. We just prevent SMP linux from using it.