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>
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 7dceea9..7fc7294 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 @@
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;
