linux-kernel - Re: [RESEND] Fast TSC calibration fails with v3.14-rc1 and later

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Date:	Wed, 12 Mar 2014 17:23:44 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	joeyli <jlee@...e.com>
cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Julian Wollrath <jwollrath@....de>, x86@...nel.org,
	LKML <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RESEND] Fast TSC calibration fails with v3.14-rc1 and later



On Wed, 12 Mar 2014, Thomas Gleixner wrote:

> On Wed, 12 Mar 2014, joeyli wrote:
> > I think maybe still using ACPI_FADT_NO_CMOS_RTC to check does
> > acpi_early_init() need run before timekeeping_init().
> > If there have any future machine that applied ACPI TAD but "Fast TSC
> > calibration" fail, at least the alternate TSC calibration can work
> > around issue.
> 
> Well, it can work around, but it sucks as it's way slower than the
> fast one. And we really don't want to pay that price for some half
> baken ACPI nonsense.
> 
> Why exactly do you need that ACPI stuff before timekeeping_init()?

According to the changelog:

    And, we want accessing ACPI TAD device to set system clock, so move
    acpi_early_init() before timekeeping_init(). This final position is
    also before efi_enter_virtual_mode().

Why do we need to access that TAD thing (whatever newfangled that is)
at this point?

Thanks,

	tglx


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