linux-kernel - Re: [PATCH 33/36] AArch64: Generic timers support

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Date:	Fri, 13 Jul 2012 12:40:03 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Marc Zyngier <marc.zyngier@....com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Deepak Saxena <dsaxena@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Walleij <linus.ml.walleij@...il.com>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org, Will Deacon <will.deacon@....com>,
	Mike Turquette <mike.turquette@...aro.org>,
	Marc Zyngier <maz@...terjones.org>
Subject: Re: [PATCH 33/36] AArch64: Generic timers support

On Thursday 12 July 2012, John Stultz wrote:
> 
> On 07/12/2012 10:31 AM, Marc Zyngier wrote:
> > On Thu, 12 Jul 2012 09:57:33 -0700, John Stultz <john.stultz@...aro.org>
> > wrote:
> >
> >> So following ia64's method is probably better then copying the 8253's
> >> rate if you're not concerned about tick-granularity error.
> > The 8253 is completely meaningless in our case (though I'm sure someone
> > could try and bold one on the side of an Aarch64 CPU...), so going the ia64
> > way is probably best (erm... this last bit doesn't sound quite right,
> > doesn't it?).
> 
> Sorry, the "copying the 8253's" bit didn't come out sarcastic enough.  :)
> 
> The best solution would be to include the actual tick-granularity, but 
> given its not really an architecture constant (which CLOCK_TICK_RATE 
> assumes), that probably wouldn't be appropriate.

Hmm, in the quest to eliminate CLOCK_TICK_RATE entirely, could we
make a Kconfig symbol that is selected for all architectures that
(may) rely on a periodic timer tick and require this to be set?

Architectures that always have a working clock source would then just
not include the timex.h header and #define ACT_HZ HZ in common code.

	Arnd
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