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>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/acpi/processor.h b/include/acpi/processor.h
index da565a48240e..a68ca8a11a53 100644
--- a/include/acpi/processor.h
+++ b/include/acpi/processor.h
@@ -48,7 +48,7 @@ struct acpi_power_register {
         u8 space_id;
         u8 bit_width;
         u8 bit_offset;
-        u8 reserved;
+        u8 access_size;
         u64 address;
 } __attribute__ ((packed));
 
@@ -63,6 +63,7 @@ struct acpi_processor_cx {
         u32 power;
         u32 usage;
         u64 time;
+        u8 bm_sts_skip;
         char desc[ACPI_CX_DESC_LEN];
 };