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

[John Linn]

> -----Original Message-----
> From: linux-arm-kernel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:linux-arm-
> kernel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Arnd Bergmann
> Sent: Monday, February 21, 2011 7:49 AM
> To: John Linn
> Cc: linux@xxxxxxxxxxxxxxxx; catalin.marinas@xxxxxxx;
> glikely@xxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> jamie@xxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> 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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