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From: Nate Lawson <nate@root.org>
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Date: Sun, 8 Jul 2012 09:49:57 -0700
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To: Andriy Gapon <avg@freebsd.org>
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Subject: Re: disabled CST_CNT write
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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.
>=20
> Could anyone with a FreeBSD laptop and non-zero CST_CNT in FADT please =
test this?

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.

-Nate