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>
diff --git a/include/acpi/processor.h b/include/acpi/processor.h
index da565a4..a68ca8a 100644
--- a/include/acpi/processor.h
+++ b/include/acpi/processor.h
@@ -48,7 +48,7 @@
u8 space_id;
u8 bit_width;
u8 bit_offset;
- u8 reserved;
+ u8 access_size;
u64 address;
} __attribute__ ((packed));
@@ -63,6 +63,7 @@
u32 power;
u32 usage;
u64 time;
+ u8 bm_sts_skip;
char desc[ACPI_CX_DESC_LEN];
};