linux-kernel - Re: [PATCH] x86/hpet: Disable HPET on Intel Coffe Lake

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Date:   Thu, 29 Aug 2019 21:45:00 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
cc:     Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, harry.pan@...el.com,
        x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH] x86/hpet: Disable HPET on Intel Coffe Lake

On Thu, 29 Aug 2019, Kai-Heng Feng wrote:
> at 20:13, Thomas Gleixner <tglx@...utronix.de> wrote:
> > On Thu, 29 Aug 2019, Kai-Heng Feng wrote:
> > 
> > > Some Coffee Lake platforms have skewed HPET timer once the SoCs entered
> > > PC10, and marked TSC as unstable clocksource as result.
> > 
> > So here you talk about Coffee Lake and in the patch you use KABYLAKE.
> 
> Coffeelake has the same model number as Kabylake.

Yeah, just a bit more text explaining that would be helpful.
 
> > > +static const struct x86_cpu_id hpet_blacklist[] __initconst = {
> > > +	{ X86_VENDOR_INTEL, 6, INTEL_FAM6_KABYLAKE_MOBILE },
> > > +	{ X86_VENDOR_INTEL, 6, INTEL_FAM6_KABYLAKE_DESKTOP },
> > 
> > So this disables HPET on all Kaby Lake variants not just on the affected
> > Coffee Lakes. I know that I rejected the initial patch with the random
> > stepping cutoff...
> > 
> >  https://lore.kernel.org/lkml/alpine.DEB.2.21.1904081403220.1748@nanos.tec.linutronix.de
> > 
> > In the other attempt to 'fix' this I asked for clarification, but silence
> > from Intel after this:
> > 
> >  https://lore.kernel.org/lkml/alpine.DEB.2.21.1905182015320.3019@nanos.tec.linutronix.de
> > 
> > Can Intel please provide some useful information about this finally?
> 
> Hopefully Intel can provide more info.
> 
> I know we should find the root cause rather than stopping at "it’s a firmware
> bug”, but users are already affected by this issue [1].
> Is there any better short-term workaround?

Not really. And if Intel stays silent, I'm just going to apply it as is
along with a stable tag.

Thanks,

	tglx