linux-kernel - Re: [patch 3/3] clockevent driver for arm/pxa2xx

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Date:	Sat, 20 Jan 2007 17:13:42 +0100
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-kernel@...r.kernel.org, mingo@...e.hu,
	Luotao Fu <lfu@...gutronix.de>
Subject: Re: [patch 3/3] clockevent driver for arm/pxa2xx

On Sat, 2007-01-20 at 17:08 +0100, Guennadi Liakhovetski wrote:
> > 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.
> 
> The thing is - 2.6.20-rc5-rt3 didn't provide clockevent on PXA, so, I took 
> Sascha's patch instead of my own, which I've been using with 2.6.18, as 
> his patches were already submitted to various lists and had chances to 
> become mainline. And strait away it didn't work. The code above seems to 
> be doing something close to Sascha's patch, so, I expect it would behave 
> in the same way. And until I introduced a minimum increment for the match 
> register, it didn't work. I either got hangs, or WARN_ON dumps about "time 
> warp detected". I think, any timer related code for PXA has to be tested 
> on real hardware under significant (real-time) load before going upstream. 
> Haven't tested -rt7 though, so, maybe it is already handled there?

No, as I'm reworking clock events a bit and I added the handling for the
match register based devices. The above will catch the event in the past
and the generic code handles that. Will be on -rt soon.

	tglx


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