linux-kernel - Re: [PATCH v2] x86: hpet: Don't default CONFIG_HPET_TIMER to be y for X86

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Date:	Fri, 28 Mar 2014 15:37:18 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	tglx@...utronix.de, mingo@...e.hu, hpa@...or.com,
	linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>,
	Clemens Ladisch <clemens@...isch.de>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH v2] x86: hpet: Don't default CONFIG_HPET_TIMER to be y
 for X86_64

Hi Ingo,

Thanks for reviewing this

On Fri, Mar 28, 2014 at 08:17:16AM +0100, Ingo Molnar wrote:
> 
> * Feng Tang <feng.tang@...el.com> wrote:
> 
> > On many new phone/tablet platforms like Baytrail/Merrifield etc, the 
> > HPET are either defeatured or has some problem to be used as a 
> > reliable timer. As these platforms also have X86_64, we should not 
> > make HPET_TIMER default y for all X86_64.
> 
> NAK!
> 
> If the HPET is unreliable on a specific platform then any of the 
> following solutions would address the problem (in order of 
> preference):
> 
>  - the hardware should not expose it. Why waste silicon on something 
>    that does not work?
> 
>  - or the firmware should not expose it. Why expose something that 
>    does not work?

Agreed, I've raised problem to BIOS vendor, but the response is very slow,
and those hardware/BIOS may already hit the market as a product.

> 
>  - or the kernel should have a quirk to reliably disable it. Why 
>    should we crash or misbehave if a driver is built into the
>    kernel?

I thought about this before, HPET doesn't have PCI ID like stuff, only
thing I can think of to identify them may be the CPU family/ID. 
Runtime check the reliability of HPET may be difficult, as we don't
know if the 8254 or the TSC are the golden timer to check HPET.

Thanks,
Feng

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