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>
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@ -145,6 +145,15 @@ int acpi_processor_ffh_cstate_probe(unsigned int cpu,
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percpu_entry->states[cx->index].eax = cx->address;
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percpu_entry->states[cx->index].ecx = MWAIT_ECX_INTERRUPT_BREAK;
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}
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/*
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* For _CST FFH on Intel, if GAS.access_size bit 1 is cleared,
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* then we should skip checking BM_STS for this C-state.
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* ref: "Intel Processor Vendor-Specific ACPI Interface Specification"
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*/
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if ((c->x86_vendor == X86_VENDOR_INTEL) && !(reg->access_size & 0x2))
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cx->bm_sts_skip = 1;
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return retval;
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}
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EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_probe);
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@ -947,7 +947,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
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if (acpi_idle_suspend)
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return(acpi_idle_enter_c1(dev, state));
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if (acpi_idle_bm_check()) {
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if (!cx->bm_sts_skip && acpi_idle_bm_check()) {
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if (dev->safe_state) {
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dev->last_state = dev->safe_state;
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return dev->safe_state->enter(dev, dev->safe_state);
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@ -48,7 +48,7 @@ struct acpi_power_register {
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u8 space_id;
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u8 bit_width;
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u8 bit_offset;
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u8 reserved;
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u8 access_size;
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u64 address;
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} __attribute__ ((packed));
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@ -63,6 +63,7 @@ struct acpi_processor_cx {
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u32 power;
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u32 usage;
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u64 time;
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u8 bm_sts_skip;
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char desc[ACPI_CX_DESC_LEN];
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};
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