disabled CST_CNT write
Andriy Gapon
avg at FreeBSD.org
Tue Jul 10 08:46:06 UTC 2012
on 08/07/2012 19:49 Nate Lawson said the following:
> 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?
>
> 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,
thank you for the information/explanation.
--
Andriy Gapon
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