disabled CST_CNT write

[Taku YAMAMOTO]

On Sun, 08 Jul 2012 12:11:32 +0300
Andriy Gapon <avg at FreeBSD.org> 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?

My Thinkpad X60 (Core 2 Duo) is such one of them.
Enabling that code makes this laptop correctly raise _CST change
notification on AC status change without a single problem.
Without enabling that, this laptop never generates such notifications.

In fact, I have been enabling that code locally for more than a couple of
years without a problem :)

In addition, that does not interfere with jkim's acpi_cx_native2.diff;
I've been enjoying MWAIT C3 with varying sleep depth based upon AC availability.

-- 
-|-__   YAMAMOTO, Taku
 | __ <     <taku at tackymt.homeip.net>

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