ACPI : Create "idle=nomwait" bootparam

"idle=nomwait" disables the use of the MWAIT
instruction from both C1 (C1_FFH) and deeper (C2C3_FFH)
C-states.

When MWAIT is unavailable, the BIOS and OS generally
negotiate to use the HALT instruction for C1,
and use IO accesses for deeper C-states.

This option is useful for power and performance
comparisons, and also to work around BIOS bugs
where broken MWAIT support is advertised.

http://bugzilla.kernel.org/show_bug.cgi?id=10807
http://bugzilla.kernel.org/show_bug.cgi?id=10914

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Li Shaohua <shaohua.li@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

2 files changed, 18 insertions, 1 deletions

diff --git a/drivers/acpi/processor_core.c b/drivers/acpi/processor_core.c
index 9a803f85ccfe..4e1bb89fd6c3 100644
--- a/drivers/acpi/processor_core.c
+++ b/drivers/acpi/processor_core.c
@@ -265,7 +265,20 @@ static int acpi_processor_set_pdc(struct acpi_processor *pr)
 
         if (!pdc_in)
                 return status;
+        if (idle_nomwait) {
+                /*
+                 * If mwait is disabled for CPU C-states, the C2C3_FFH access
+                 * mode will be disabled in the parameter of _PDC object.
+                 * Of course C1_FFH access mode will also be disabled.
+                 */
+                union acpi_object *obj;
+                u32 *buffer = NULL;
 
+                obj = pdc_in->pointer;
+                buffer = (u32 *)(obj->buffer.pointer);
+                buffer[2] &= ~(ACPI_PDC_C_C2C3_FFH | ACPI_PDC_C_C1_FFH);
+
+        }
         status = acpi_evaluate_object(pr->handle, "_PDC", pdc_in, NULL);
 
         if (ACPI_FAILURE(status))
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index c75c7ace8c13..d592dbb1d12a 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -957,13 +957,17 @@ static int acpi_processor_get_power_info_cst(struct acpi_processor *pr)
                         } else {
                                 continue;
                         }
-                        if (cx.type == ACPI_STATE_C1 && idle_halt) {
+                        if (cx.type == ACPI_STATE_C1 &&
+                                        (idle_halt || idle_nomwait)) {
                                 /*
                                  * In most cases the C1 space_id obtained from
                                  * _CST object is FIXED_HARDWARE access mode.
                                  * But when the option of idle=halt is added,
                                  * the entry_method type should be changed from
                                  * CSTATE_FFH to CSTATE_HALT.
+                                 * When the option of idle=nomwait is added,
+                                 * the C1 entry_method type should be
+                                 * CSTATE_HALT.
                                  */
                                 cx.entry_method = ACPI_CSTATE_HALT;
                                 snprintf(cx.desc, ACPI_CX_DESC_LEN, "ACPI HLT");