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From: David Brownell <david-b@pacbell.net>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Subject: Re: 2.6.20-mm2
Date: Thu, 22 Feb 2007 14:17:31 -0800
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Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
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On Thursday 22 February 2007 12:33 am, Rafael J. Wysocki wrote:

> Unfortunately, the userland shipped with OpenSUSE refuses to talk to the new
> one (or I don't know how to make it do that).

Did your "udev" create a /dev/rtc0?  If not, /sys/class/rtc-dev/rtc0/dev
will give the right major/minor numbers.

Given a /dev/rtc0, there are two simple solutions:

  (a) ln -s /dev/rtc0 /dev/rtc
  (b) upgrade your "hwclock" to one supporting "hwclock --file /dev/rtc0",
      since that should also try rtc0 when rtc can't be opened.

I found a udev incantation "git whatchanged drivers/rtc/rtc-dev.c",
which can automate (a):

       KERNEL=="rtc0", SYMLINK+="rtc"

I'm not sure what the story is on hwclock updates, given the issue
with "util-linux" maintainership.  I sent a patch on 7-Aug-2006 to
Adrian Bunk, which appears to have been disregarded, then to Karel
Zak (for the new fork?) on 17-Nov-2006 ... but if there's been an
announcement about a new util-linux repository with that patch,
I missed it.  The busybox patch I submitted 26-Jan-2007 hasn't
yet been merged, but that's a lot more understandable.

Basically it looks like userspace is almost a year behind the kernel
support for this RTC framework.  The problematic part is that it
seems that the "util-linux" maintainership issues are preventing
that issue from getting resolved ... so for now, I usually use
workaround (a).


> > Shoot.  OK, I'll see if I can reproduce it myself.  Is this system
> > using a generic CMOS RTC?  Or is HPET somehow involved?  (That old
> > RTC driver has HPET voodoo as well as normal RTC stuff.)
> 
> How can I check that?

If your boot messages say things about HPET, that's a start.  :)
I don't really know HPET; it hasn't ever come up on any system
that I've used.  ISTR that for various reasons BIOS would hide
it on most systems, but that Linux has been working on un-hiding
that hardware so it could be used.  I'll read up on it.  (As I
implied, the source code comments leave a lot to be desired.)

- Dave
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