From owner-svn-src-head@FreeBSD.ORG  Mon May 20 02:21:01 2013
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Date: Mon, 20 May 2013 02:21:00 +0000
From: Alexey Dokuchaev <danfe@FreeBSD.org>
To: Warner Losh <imp@FreeBSD.org>
Subject: Re: svn commit: r247086 - head/sys/x86/isa
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 <20130221064912.GA20360@FreeBSD.org>
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On Thu, Feb 21, 2013 at 06:49:12AM +0000, Alexey Dokuchaev wrote:
> On Thu, Feb 21, 2013 at 06:38:24AM +0000, Warner Losh wrote:
> > New Revision: 247086
> > URL: http://svnweb.freebsd.org/changeset/base/247086
> > 
> > Log:
> >   Correct comment about use of pmtimer, and the real reason it isn't
> >   used or desirable for amd64.
> 
> Thanks!
> 
> > + * pmtimer is used only with the old APM power management, and not with
> > + * acpi, which is required for amd64, so skip it in that case.
> 
> Does it also mean it should be removed from ACPI-driven i386 machines kernel
> configs?

Apparently not: I've been running FreeBSD 8.4-PRERELEASE without pmtimer for
a while, and noticed that my laptop stops keeping time during suspend.  I've
never noticed that behavior before (presumably, with pmtimer).

I've found this old thread [1] on -current@ from Jan 2001 where src/UPDATING
is quoted:

    The new pmtimer device is necessary for laptops.  Failure to
    include the device will cause suspended laptops losing time
    when they resume.

I will soon rebuild the kernel and put pmtimer back to see it fixes time
keeping for me.  If it will, apparently it is still useful for i386, and
not just for APM, but ACPI as well...

./danfe

[1] http://www.mail-archive.com/freebsd-current@freebsd.org/msg23642.html