[RFC/PATCH 1/2] cpuidle: Allow idle-states to be disabled at start

[Gautham R. Shenoy]

From: "Gautham R. Shenoy" <ego at linux.vnet.ibm.com>

Currently all the idle states registered by a cpu-idle driver are
enabled by default. This patch adds a mechanism which allows the
driver to hint if an idle-state should start in a disabled state. The
cpu-idle core will use this hint to appropriately initialize the
usage->disable knob of the CPU device idle state.

The state can be enabled at run time by echo'ing a zero to the sysfs
"disable" control file.

Signed-off-by: Gautham R. Shenoy <ego at linux.vnet.ibm.com>
---
 drivers/cpuidle/cpuidle.c | 7 +++++++
 include/linux/cpuidle.h   | 7 ++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index c73207a..b4debc7 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -439,7 +439,14 @@ static void __cpuidle_unregister_device(struct cpuidle_device *dev)
 
 static void __cpuidle_device_init(struct cpuidle_device *dev)
 {
+	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
+	int i;
+
 	memset(dev->states_usage, 0, sizeof(dev->states_usage));
+	for (i = 0; i < drv->state_count; i++) {
+		if (drv->states[i].disable_use_at_start)
+			dev->states_usage[i].disable = 1;
+	}
 	dev->last_residency = 0;
 }
 
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index bb31373..f3fe855 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -44,7 +44,12 @@ struct cpuidle_state {
 	int		power_usage; /* in mW */
 	unsigned int	target_residency; /* in US */
 	bool		disabled; /* disabled on all CPUs */
-
+	/*
+	 * disable_use_at_start: If true, then this idle state will be
+	 * disabled by default. It can be enabled at runtime using the
+	 * per-cpu cpuidle sysfs control file named "disable".
+	 */
+	bool            disable_use_at_start;
 	int (*enter)	(struct cpuidle_device *dev,
 			struct cpuidle_driver *drv,
 			int index);
-- 
1.9.4