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, 16 insertions, 1 deletions

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 7dceea947232..7fc729498760 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -7,6 +7,10 @@
 #include <linux/module.h>
 #include <linux/pm.h>
 #include <linux/clockchips.h>
+#include <asm/system.h>
+
+unsigned long idle_halt;
+EXPORT_SYMBOL(idle_halt);
 
 struct kmem_cache *task_xstate_cachep;
 
@@ -325,7 +329,18 @@ static int __init idle_setup(char *str)
                 pm_idle = poll_idle;
         } else if (!strcmp(str, "mwait"))
                 force_mwait = 1;
-        else
+        else if (!strcmp(str, "halt")) {
+                /*
+                 * When the boot option of idle=halt is added, halt is
+                 * forced to be used for CPU idle. In such case CPU C2/C3
+                 * won't be used again.
+                 * To continue to load the CPU idle driver, don't touch
+                 * the boot_option_idle_override.
+                 */
+                pm_idle = default_idle;
+                idle_halt = 1;
+                return 0;
+        } else
                 return -1;
 
         boot_option_idle_override = 1;