linux-kernel - Re: [PATCH v2 4/9] clocksource/cadence_ttc: Use enable/disable

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Date:	Sat, 7 Dec 2013 11:56:06 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>
cc:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Russell King <linux@....linux.org.uk>,
	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v2 4/9] clocksource/cadence_ttc: Use enable/disable_irq

On Fri, 6 Dec 2013, Sören Brinkmann wrote:
> On Thu, Nov 28, 2013 at 08:07:10PM +0100, Thomas Gleixner wrote:
> > There is a solution to this. We can identify the broadcast device in
> > the core and serialize all callers including interrupts on a different
> > cpu against the update. So no need for the disable/enable_irq() dance.
> 
> IIUC, and please correct me if I'm wrong, with the patch I'd simply call
> 'clockevents_update_freq() without having to disable IRQs. But I'm not
> sure whether periodic mode is covered. I found, that I had to reprogram
> the timer interval in my clock notifier callback when the timer
> frequency changes. I think 'clockevents_update_freq()' only handles
> oneshot mode. For that reason I call 'ttc_set_interval()' in the clock
> notifier in case the timer is in periodic mode. For that call we'd still
> have possible races. I guess the best solution would be to move that
> functionality into 'clockevents_update_freq()'?

Indeed.