disabled CST_CNT write

[Ian Smith]

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