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Subject: Re: [PATCH] x86/hpet: Disable HPET on Intel Coffe Lake
From:   Kai-Heng Feng <kai.heng.feng@canonical.com>
In-Reply-To: <alpine.DEB.2.21.1908291351510.1938@nanos.tec.linutronix.de>
Date:   Thu, 29 Aug 2019 22:13:32 +0800
Cc:     Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, harry.pan@intel.com,
        x86@kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>
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Message-Id: <793CCD4F-35E0-46B9-B5D4-3D3233BA5D35@canonical.com>
References: <20190829091232.15065-1-kai.heng.feng@canonical.com>
 <alpine.DEB.2.21.1908291351510.1938@nanos.tec.linutronix.de>
To:     Thomas Gleixner <tglx@linutronix.de>
Sender: linux-kernel-owner@vger.kernel.org
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at 20:13, Thomas Gleixner <tglx@linutronix.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.

>
>> 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:

Ok.

>
>> +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?

[1] https://bugzilla.kernel.org/show_bug.cgi?id=204537

Kai-Heng

>
> Thanks,
>
> 	tglx