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, 3 insertions, 1 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 312fe77764a4..65db7f4711aa 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -818,7 +818,7 @@ and is between 256 and 4096 characters. It is defined in the file
                         See Documentation/ide/ide.txt.
 
         idle=           [X86]
-                        Format: idle=poll or idle=mwait
+                        Format: idle=poll or idle=mwait, idle=halt
                         Poll forces a polling idle loop that can slightly improves the performance
                         of waking up a idle CPU, but will use a lot of power and make the system
                         run hot. Not recommended.
@@ -826,6 +826,8 @@ and is between 256 and 4096 characters. It is defined in the file
                         to not use it because it doesn't save as much power as a normal idle
                         loop use the MONITOR/MWAIT idle loop anyways. Performance should be the same
                         as idle=poll.
+                        idle=halt. Halt is forced to be used for CPU idle.
+                        In such case C2/C3 won't be used again.
 
         ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
                         Claim all unknown PCI IDE storage controllers.