disabled CST_CNT write
Moore, Robert
robert.moore at intel.com
Mon Jul 9 19:02:44 UTC 2012
> This Thinkpad T23 with latest (Oct2006) BIOS & EC shows no FADT .. but
> FACP has CST_CNT=0xf4. Is that relevant at all?
An oddity of ACPI -- the FADT has the signature "FACP".
> -----Original Message-----
> From: owner-freebsd-acpi at freebsd.org [mailto:owner-freebsd-
> acpi at freebsd.org] On Behalf Of Ian Smith
> Sent: Monday, July 09, 2012 9:06 AM
> To: Nate Lawson
> Cc: freebsd-acpi at freebsd.org; Andriy Gapon
> Subject: Re: disabled CST_CNT write
>
> On Sun, 8 Jul 2012 09:49:57 -0700, Nate Lawson wrote:
> > On Jul 8, 2012, at 2:11 AM, Andriy Gapon wrote:
> >
> > > acpi_cpu.c has a block of code to write CST_CNT to SMI_CMD, but
> the block is > > under #ifdef notyet. It seems that the code was
> added that many years ago and > > never enabled.
> > > Now, judging from the reports I've seen on this mailing list, it
> appears that > > _CST changes do happen and the driver seem to handle
> them sufficiently well.
> > > I think that a lot of modern platforms do not even provide CST_CNT
> and assume > > that an OS is able to handle C-state change
> notifications.
> > > So, I guess that it should be safe to enable the code in question
> now.
> > >
> > > Could anyone with a FreeBSD laptop and non-zero CST_CNT in FADT >
> > please test this?
>
> This Thinkpad T23 with latest (Oct2006) BIOS & EC shows no FADT .. but
> FACP has CST_CNT=0xf4. Is that relevant at all?
>
> > It was only under an #ifdef because at the time our CST >
> implementation couldn't handle CST changes cleanly. I had added some >
> support for it, but since it couldn't be tested, I wasn't sure how >
> actual hardware would behave.
> >
> > I think it's fine to enable now. I think 2007-era Thinkpads were
> some > of the first to add this feature.
>
> T43? Maybe it's time I upgraded :)
>
> cheers, Ian
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