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

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Message-Id: <A863DF08-2275-4FEA-9A0D-44C5D4807458@canonical.com>
Date:   Tue, 1 Oct 2019 23:47:09 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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

Hi Thomas,

> On Aug 30, 2019, at 03:45, Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> 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.

Seems like there's still no updates from Intel. Can we have this patch in v5.4?

Kai-Heng

> 
> Thanks,
> 
> 	tglx