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

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Date:   Thu, 29 Aug 2019 14:13:53 +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:

> 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. 

> Harry Pan identified it's a firmware bug [1].
> 
> To prevent creating a circular dependency between HPET and TSC, let's
> disable HPET on affected platforms.
> 
> [1]: https://lore.kernel.org/lkml/20190516090651.1396-1-harry.pan@intel.com/
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203183

Please use Link:// for reference not [1] and not Bugzilla:

> +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?

Thanks,

	tglx