Messages in this thread | | | Subject | Re: [PATCH] HPET: Workaround for a BIOS workaround on AMD SB700 platform | From | crane cai <> | Date | Thu, 14 Aug 2008 17:10:24 +0800 |
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On Thu, 2008-08-14 at 10:41 +0200, Ingo Molnar wrote: > * crane cai <crane.cai@amd.com> wrote: > > > >From 9bd2f534f986768f1944e626e37af1c323e47dbb Mon Sep 17 00:00:00 2001 > > From: Crane Cai <crane.cai@amd.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@amd.com> > > Signed-off-by: Crane Cai <crane.cai@amd.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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