From: Len Brown <len.brown@xxxxxxxxx> upstream 718be4aaf3613cf7c2d097f925abc3d3553c0605 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@xxxxxxxxx> --- this backport applies cleanly to 2.6.32.y. It applies w/ a small offset to 2.6.33.y and 2.34.y 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(-) Index: linux-2.6.32.y/arch/x86/kernel/acpi/cstate.c =================================================================== --- linux-2.6.32.y.orig/arch/x86/kernel/acpi/cstate.c +++ linux-2.6.32.y/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); Index: linux-2.6.32.y/drivers/acpi/processor_idle.c =================================================================== --- linux-2.6.32.y.orig/drivers/acpi/processor_idle.c +++ linux-2.6.32.y/drivers/acpi/processor_idle.c @@ -962,7 +962,7 @@ 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); Index: linux-2.6.32.y/include/acpi/processor.h =================================================================== --- linux-2.6.32.y.orig/include/acpi/processor.h +++ linux-2.6.32.y/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]; -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
