idle, x86: Allow off-lined CPU to enter deeper C states

Currently when a CPU is off-lined it enters either MWAIT-based idle or,
if MWAIT is not desired or supported, HLT-based idle (which places the
processor in C1 state). This patch allows processors without MWAIT
support to stay in states deeper than C1.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@amd.com>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index f7cab5e9c4d6..3e146b2ada4a 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -72,6 +72,34 @@ typedef int (*cpuidle_enter_t)(struct cpuidle_device *dev,
 static cpuidle_enter_t cpuidle_enter_ops;
 
 /**
+ * cpuidle_play_dead - cpu off-lining
+ *
+ * Only returns in case of an error
+ */
+int cpuidle_play_dead(void)
+{
+        struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
+        struct cpuidle_driver *drv = cpuidle_get_driver();
+        int i, dead_state = -1;
+        int power_usage = -1;
+
+        /* Find lowest-power state that supports long-term idle */
+        for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
+                struct cpuidle_state *s = &drv->states[i];
+
+                if (s->power_usage < power_usage && s->enter_dead) {
+                        power_usage = s->power_usage;
+                        dead_state = i;
+                }
+        }
+
+        if (dead_state != -1)
+                return drv->states[dead_state].enter_dead(dev, dead_state);
+
+        return -ENODEV;
+}
+
+/**
  * cpuidle_idle_call - the main idle loop
  *
  * NOTE: no locks or semaphores should be used here