From 718be4aaf3613cf7c2d097f925abc3d3553c0605 Mon Sep 17 00:00:00 2001 From: Len Brown Date: Thu, 22 Jul 2010 16:54:27 -0400 Subject: 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 --- 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(-) diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c index 2e837f5080f..fb7a5f052e2 100644 --- a/arch/x86/kernel/acpi/cstate.c +++ b/arch/x86/kernel/acpi/cstate.c @@ -145,6 +145,15 @@ int acpi_processor_ffh_cstate_probe(unsigned int cpu, 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); diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c index b1b385692f4..b351342f1fa 100644 --- a/drivers/acpi/processor_idle.c +++ b/drivers/acpi/processor_idle.c @@ -947,7 +947,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev, 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); diff --git a/include/acpi/processor.h b/include/acpi/processor.h index da565a48240..a68ca8a11a5 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]; }; -- cgit v1.2.3-18-g5258