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Re: Would setting the CONFIG_RTC option break the powerpc kernel on your machine ?

On Wed, 2003-12-17 at 18:17, Lee Braiden wrote:
> On Wednesday 17 Dec 2003 6:24 am, Benjamin Herrenschmidt wrote:
> > CONFIG_RTC will definitely break a pmac
> I think I heard something about clock/timer problems on PPC a long time ago, 
> but could never track down an issue.  Wouldn't it be best to remove RTC on 
> PPC or document the problem with a (read help) or something?
> Is the PPC RTC (as opposed to GENERIC_RTC) stuff automatically in there, or 
> something?  Or is it this PPC_RTC that's broken?

Well... CONFIG_RTC enables the "PC style" RTC driver that taps IO ports
to look for an RTC chip of the kind found in x86 machines. Such a chip
doesn't exist on powermac and this random IO port tapping can actually
crash the machine.

CONFIG_PPC_RTC/CONFIG_GENERIC_RTC is a different driver that provides
the /dev/rtc interface but relies on hooks provided by the platform
code for actually getting/setting the RTC content. The PowerMac platform
provides hooks for the different kind of RTC chips found on Macs (that
is basically  access to the RTC via via-cuda or via-pmu). CHRP or
PReP machines should provide their own hooks, it's possible that what
CHRP provides doesn't work properly on the Pegasos, in which case we'd
have to fix this.


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