ACPI: Create "idle=halt" bootparam

"idle=halt" limits the idle loop to using
the halt instruction.  No MWAIT, no IO accesses,
no C-states deeper than C1.

If something is broken in the idle code,
"idle=halt" is a less severe workaround
than "idle=poll" which disables all power savings.

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

1 files changed, 22 insertions, 0 deletions

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 0fc310e7dfd6..c75c7ace8c13 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -41,6 +41,7 @@
 #include <linux/pm_qos_params.h>
 #include <linux/clockchips.h>
 #include <linux/cpuidle.h>
+#include <linux/cpuidle.h>
 
 /*
  * Include the apic definitions for x86 to have the APIC timer related defines
@@ -57,6 +58,7 @@
 
 #include <acpi/acpi_bus.h>
 #include <acpi/processor.h>
+#include <asm/processor.h>
 
 #define ACPI_PROCESSOR_COMPONENT        0x01000000
 #define ACPI_PROCESSOR_CLASS            "processor"
@@ -955,6 +957,17 @@ static int acpi_processor_get_power_info_cst(struct acpi_processor *pr)
                         } else {
                                 continue;
                         }
+                        if (cx.type == ACPI_STATE_C1 && idle_halt) {
+                                /*
+                                 * 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.
+                                 */
+                                cx.entry_method = ACPI_CSTATE_HALT;
+                                snprintf(cx.desc, ACPI_CX_DESC_LEN, "ACPI HLT");
+                        }
                 } else {
                         snprintf(cx.desc, ACPI_CX_DESC_LEN, "ACPI IOPORT 0x%x",
                                  cx.address);
@@ -1780,6 +1793,15 @@ int __cpuinit acpi_processor_power_init(struct acpi_processor *pr,
                 return 0;
 
         if (!first_run) {
+                if (idle_halt) {
+                        /*
+                         * When the boot option of "idle=halt" is added, halt
+                         * is used for CPU IDLE.
+                         * In such case C2/C3 is meaningless. So the max_cstate
+                         * is set to one.
+                         */
+                        max_cstate = 1;
+                }
                 dmi_check_system(processor_power_dmi_table);
                 max_cstate = acpi_processor_cstate_check(max_cstate);
                 if (max_cstate < ACPI_C_STATES_MAX)