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

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Date:	Thu, 14 Aug 2008 17:10:24 +0800
From:	crane cai <crane.cai@....com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	vojtech@...e.cz, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	XiaoGang Zheng <gang.zheng@....com>
Subject: Re: [PATCH] HPET: Workaround for a BIOS workaround on AMD SB700
	platform


On Thu, 2008-08-14 at 10:41 +0200, Ingo Molnar wrote:
> * crane cai <crane.cai@....com> 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.
> >
> > 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.
> >
> > 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.
> 
> nice fix! I've applied it to tip/x86/urgent as the quirk is limited to 
> this platform so it should be safe for v2.6.27 as well.
> 
> Exactly what kind of failure mode have you seen without the quirk? Do we 
> read out the wrong values and thus hpet_clocksource_register() is 
> calibrated incorrectly and you can get non-functional high-res timers? 
> Have you seen hangs/crashes due to that, or incorrect timings?
System might loop in TSC calibration in booting. System tick can not correctly set.

> > Signed-off-by: XiaoGang Zheng <gang.zheng@....com>
> > Signed-off-by: Crane Cai <crane.cai@....com>
> 
> A quick question: the signoff order indicates that the patch has been 
> authored by XiaoGang Zheng. Or is the reverse order intended? (you wrote 
> the patch and XiaoGang Zheng processed it further)
XiaoGang insures that HPET check method in hardware view.
I refine the method and generate the patch.
Vojtech and Zahir refine the description.
This issue is cleared by Joachim and many other persons in SUSE.
Thanks all.

> 
> 	Ingo
> 

-Crane

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