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Date: Sun, 08 Jul 2012 12:11:32 +0300
From: Andriy Gapon <avg@FreeBSD.org>
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Subject: disabled CST_CNT write
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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?
Thank you.
-- 
Andriy Gapon