linux-kernel - Re: [PATCH 04/27] asm-generic: add legacy I/O header files

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Date:	Fri, 1 May 2009 14:09:04 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Russell King <rmk+lkml@....linux.org.uk>
Cc:	Michal Simek <monstr@...str.eu>, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org,
	Remis Lima Baima <remis.developer@...glemail.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/27] asm-generic: add legacy I/O header files

On Fri, 1 May 2009 13:37:28 +0100
Russell King <rmk+lkml@....linux.org.uk> wrote:

> On Fri, May 01, 2009 at 02:25:14PM +0200, Michal Simek wrote:
> > Arnd Bergmann wrote:
> > > On Friday 01 May 2009, Michal Simek wrote:
> > >>> +/*
> > >>> + * CLOCK_TICK_RATE is highly PC-specific and should not
> > >>> + * be used in portable code. 1193182 is the value for the
> > >>> + * original i8253 PIC.
> > >>> + */
> > >>> +#ifndef CLOCK_TICK_RATE
> > >>> +#define CLOCK_TICK_RATE                1193182
> > >>> +#endif
> > >>
> > >> Why is this in generic code?
> > > 
> > > CLOCK_TICK_RATE is only used in a few places:

Joining in late but its not at all highly PC specific. The same frequency
is used for a whole pile of setups (Alpha etc). It's not well named but
there are good sound reasons the PC chose 1193182 and while those reasons
have long lapsed its a good frequency for other reasons nowdays.

The clock isn't for the PIC either - its for the PIT (although its used
to clock various other things).

We actually have a define of PIT_TICK_RATE internal to the x86 port for
those x86 cases that can use it.





Alan
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