linux-kernel - RE: [PATCH V4 3/4] ARM: Xilinx: base header files and assembly macros

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Date:	Mon, 21 Feb 2011 08:04:38 -0700
From:	John Linn <John.Linn@...inx.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux@....linux.org.uk>, <catalin.marinas@....com>,
	<glikely@...retlab.ca>, <linux-kernel@...r.kernel.org>,
	<jamie@...ieiles.com>, <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH V4 3/4] ARM: Xilinx: base header files and assembly macros

> -----Original Message-----
> From: linux-arm-kernel-bounces@...ts.infradead.org [mailto:linux-arm-
> kernel-bounces@...ts.infradead.org] On Behalf Of Arnd Bergmann
> Sent: Monday, February 21, 2011 7:49 AM
> To: John Linn
> Cc: linux@....linux.org.uk; catalin.marinas@....com;
> glikely@...retlab.ca; linux-kernel@...r.kernel.org;
> jamie@...ieiles.com; linux-arm-kernel@...ts.infradead.org
> Subject: Re: [PATCH V4 3/4] ARM: Xilinx: base header files and
assembly
> macros
> 
> On Monday 21 February 2011, John Linn wrote:
> > > It would be better if you could avoid introducing new uses of
> > > CLOCK_TICK_RATE, because that will have to be removed before we
can
> > > move to a real multi-platform kernel. For instance, you can put
> > > PERIPHERAL_CLOCK_RATE in a hardware specific header and put a
bogus
> > > definition for CLOCK_TICK_RATE into timex.h
> >
> > Hi Arnd,
> >
> > I can remove the use of it from my timer code, but I still see
> > CLOCK_TICK_RATE
> > being used in linux/jiffies.h.
> >
> > I tried removing it and got build errors.  Am I missing something
> there?
> >
> 
> You still need to have some definition for CLOCK_TICK_RATE to make
> the jiffies code compile, but the actual value no longer matters.

I see. Now that I re-read your last response I get that from it.

> 
> Traditionally, this was the i386-style PIT timer frequency of 11.93
MHz
> for some things and the actual timer frequency for other things.
> The timer code tries to correct the jiffies value based on difference
> between the intended HZ frequency (100, 250 or 1000) and the actual
> on (something very close to that, but not exact).
> 
> You can e.g. set it to (100 * HZ) to make something up that won't
> hurt in that calculation.
> 

Gotcha. I now understand to stay away from using CLOCK_TICK_RATE.

Sounds like it's worth a comment in mach/timex.h that says it's not 
really used as it seems a bit misleading for others.

Thanks,
John

> 	Arnd
> 
> _______________________________________________
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