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From: Greg KH on 30 Jul 2010 14:20
2.6.34-stable review patch. If anyone has any objections, please let us know.

------------------

From: Len Brown <len.brown(a)intel.com>

commit 718be4aaf3613cf7c2d097f925abc3d3553c0605 upstream.

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(a)intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
arch/x86/kernel/acpi/cstate.c | 9 +++++++++
drivers/acpi/processor_idle.c | 2 +-
include/acpi/processor.h | 3 ++-
3 files changed, 12 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/acpi/cstate.c
+++ b/arch/x86/kernel/acpi/cstate.c
@@ -145,6 +145,15 @@ int acpi_processor_ffh_cstate_probe(unsi
percpu_entry->states[cx->index].eax = cx->address;
percpu_entry->states[cx->index].ecx = MWAIT_ECX_INTERRUPT_BREAK;
}
+
+ /*
+ * For _CST FFH on Intel, if GAS.access_size bit 1 is cleared,
+ * then we should skip checking BM_STS for this C-state.
+ * ref: "Intel Processor Vendor-Specific ACPI Interface Specification"
+ */
+ if ((c->x86_vendor == X86_VENDOR_INTEL) && !(reg->access_size & 0x2))
+ cx->bm_sts_skip = 1;
+
return retval;
}
EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_probe);
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -955,7 +955,7 @@ static int acpi_idle_enter_bm(struct cpu
if (acpi_idle_suspend)
return(acpi_idle_enter_c1(dev, state));

- if (acpi_idle_bm_check()) {
+ if (!cx->bm_sts_skip && acpi_idle_bm_check()) {
if (dev->safe_state) {
dev->last_state = dev->safe_state;
return dev->safe_state->enter(dev, dev->safe_state);
--- 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));

@@ -74,6 +74,7 @@ struct acpi_processor_cx {
u32 power;
u32 usage;
u64 time;
+ u8 bm_sts_skip;
struct acpi_processor_cx_policy promotion;
struct acpi_processor_cx_policy demotion;
char desc[ACPI_CX_DESC_LEN];


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