linux-kernel - Re: [PATCH] HPET: Workaround for a BIOS workaround on AMD SB700 platform

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Message-ID: <20080814141439.GA14027@suse.cz>
Date:	Thu, 14 Aug 2008 16:14:39 +0200
From:	Vojtech Pavlik <vojtech@...e.cz>
To:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
Cc:	crane cai <crane.cai@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] HPET: Workaround for a BIOS workaround on AMD SB700
	platform

On Thu, Aug 14, 2008 at 10:11:56AM -0400, Lennart Sorensen wrote:
> On Thu, Aug 14, 2008 at 11:13:36AM +0800, crane cai wrote:
> > >From 9bd2f534f986768f1944e626e37af1c323e47dbb Mon Sep 17 00:00:00 2001
> > From: Crane Cai <crane.cai@....com>
> > Date: Thu, 14 Aug 2008 10:31:01 +0800
> > Subject: [PATCH] HPET: Workaround for a BIOS workaround on AMD SB700 platform
> > 
> > On the AMD SB700 southbridge, between the revisions 0x30 to 0x3a, when its
> > spread-spectrum frequency modulation feature is enabled, the base frequency
> > used by the HPET will not be running on average slower than nominal 14.318
> > MHz.
> 
> Should that have read "the base frequency used by HPET will on average
> be running slower than nominal 14.318 MHz"?  That would be pretty much
> the opposite of what the comment says, but makes more sense based on the
> rest of the comment, and is a lot simpler to parse.

Yes, that is the case.

> > Since there is no provision in the OS for HPET to work with properly with
> > slower frequency, the BIOS on this platform uses SMM to emulate accesses to
> > the HPET config register to supply a corrected base frequency to compensate
> > for it.
> 
> Seems to have an extra "with" in front of properly.
> 
> > However, due to the implementation of the SMM BIOS code, there is a time
> > window after the first access to the HPET, which triggers initialization of
> > the SMM code, in which the HPET isn't available. Thus it's necessary to wait
> > until the HPET emulation is ready, and this is what the patch does on the
> > affected machines.

-- 
Vojtech Pavlik
Director SuSE Labs
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