From: Len Brown <len.brown@intel.com>
Date: Thu, 22 Jul 2010 20:54:27 +0000 (-0400)
Subject: ACPI: skip checking BM_STS if the BIOS doesn't ask for it
X-Git-Tag: v2.6.35~38^2~2^2~1
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=718be4aaf3613cf7c2d097f925abc3d3553c0605;p=pandora-kernel.git

ACPI: skip checking BM_STS if the BIOS doesn't ask for it

It turns out that there is a bit in the _CST for Intel FFH C3
that tells the OS if we should be checking BM_STS or not.

Linux has been unconditionally checking BM_STS.
If the chip-set is configured to enable BM_STS,
it can retard or completely prevent entry into
deep C-states -- as illustrated by turbostat:

http://userweb.kernel.org/~lenb/acpi/utils/pmtools/turbostat/

ref: Intel Processor Vendor-Specific ACPI Interface Specification
table 4 "_CST FFH GAS Field Encoding"
Bit 1: Set to 1 if OSPM should use Bus Master avoidance for this C-state

https://bugzilla.kernel.org/show_bug.cgi?id=15886

Signed-off-by: Len Brown <len.brown@intel.com>
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