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

Arnd Bergmann
2009-05-01T13:30:21Z

On Friday 01 May 2009, Alan Cox wrote:
> 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.

How about this comment then:

/*
* CLOCK_TICK_RATE is traditionally the base frequency using the PC-style
* i8253 "PIT" timer. Architecture independent device drivers should not
* rely on this value.
* Any architecture that either has a real PC-style PIT, or does not have a
* fixed timer interval at all and just needs to provide some value here
* should just fall back to this default.
*/