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authorLen Brown <len.brown@intel.com>2010-07-22 16:54:27 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2010-08-02 10:30:11 -0700
commitfac0c3bf65fbb1a29cf603909fde5a71ca7981cd (patch)
tree9996a83fc663cd9d0889b276e7413362d004feb3 /arch/x86/kernel/acpi/cstate.c
parent989e4282b0d74ccd334e5049e51a4ac80e17166a (diff)
ACPI: skip checking BM_STS if the BIOS doesn't ask for it
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>
Diffstat (limited to 'arch/x86/kernel/acpi/cstate.c')
-rw-r--r--arch/x86/kernel/acpi/cstate.c9
1 files changed, 9 insertions, 0 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);