| From 718be4aaf3613cf7c2d097f925abc3d3553c0605 Mon Sep 17 00:00:00 2001 |
| From: Len Brown <len.brown@intel.com> |
| Date: Thu, 22 Jul 2010 16:54:27 -0400 |
| Subject: ACPI: skip checking BM_STS if the BIOS doesn't ask for it |
| |
| From: Len Brown <len.brown@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@intel.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@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 |
| @@ -954,7 +954,7 @@ 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]; |