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Subject: Re: [patch 3/3] clockevent driver for arm/pxa2xx
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Cc: Sascha Hauer <s.hauer@pengutronix.de>, linux-kernel@vger.kernel.org,
       mingo@elte.hu, Luotao Fu <lfu@pengutronix.de>
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Date: Fri, 19 Jan 2007 20:33:40 +0100
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On Fri, 2007-01-19 at 20:13 +0100, Guennadi Liakhovetski wrote:
> > +static u32 clockevent_mode = 0;
> > +
> > +static void pxa_set_next_event(unsigned long evt,
> > +				  struct clock_event_device *unused)
> > +{
> > +	OSMR0 = OSCR + evt;
> > +}
> 
> This doesn't work for me in various nasty ways. Please, check for a 
> minimum delay or loop to get ahead of time. See code in the "old" timer 
> ISR. See how it unconditionally adds at least 10 ticks...

I added support for match register based devices and you want to do
something like this:

static int hpet_next_event(unsigned long delta,
                           struct clock_event_device *evt)
{
        unsigned long cnt;

        cnt = hpet_readl(HPET_COUNTER);
        cnt += delta;
        hpet_writel(cnt, HPET_T0_CMP);

        return ((long)(hpet_readl(HPET_COUNTER) - cnt ) > 0);
}

The generic code takes care of the already expired event.

	tglx