Merge tag 'suspend-to-idle-3.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm

Pull suspend-to-idle updates from Rafael Wysocki:
 "Suspend-to-idle timer quiescing support for v3.20-rc1

  Until now suspend-to-idle has not been able to save much more energy
  than runtime PM because of timer interrupts that periodically bring
  CPUs out of idle while they are waiting for a wakeup interrupt.  Of
  course, the timer interrupts are not wakeup ones, so the handling of
  them can be deferred until a real wakeup interrupt happens, but at the
  same time we don't want to mass-expire timers at that point.

  The solution is to suspend the entire timekeeping when the last CPU is
  entering an idle state and resume it when the first CPU goes out of
  idle.  That has to be done with care, though, so as to avoid accessing
  suspended clocksources etc.  end we need extra support from idle
  drivers for that.

  This series of commits adds support for quiescing timers during
  suspend-to-idle and adds the requisite callbacks to intel_idle and the
  ACPI cpuidle driver"

* tag 'suspend-to-idle-3.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
  ACPI / idle: Implement ->enter_freeze callback routine
  intel_idle: Add ->enter_freeze callbacks
  PM / sleep: Make it possible to quiesce timers during suspend-to-idle
  timekeeping: Make it safe to use the fast timekeeper while suspended
  timekeeping: Pass readout base to update_fast_timekeeper()
  PM / sleep: Re-implement suspend-to-idle handling

1 files changed, 68 insertions, 26 deletions

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 125150dc6e81..4d534582514e 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -19,6 +19,8 @@
 #include <linux/ktime.h>
 #include <linux/hrtimer.h>
 #include <linux/module.h>
+#include <linux/suspend.h>
+#include <linux/tick.h>
 #include <trace/events/power.h>
 
 #include "cpuidle.h"
@@ -32,7 +34,6 @@ LIST_HEAD(cpuidle_detected_devices);
 static int enabled_devices;
 static int off __read_mostly;
 static int initialized __read_mostly;
-static bool use_deepest_state __read_mostly;
 
 int cpuidle_disabled(void)
 {
@@ -66,36 +67,23 @@ int cpuidle_play_dead(void)
 }
 
 /**
- * cpuidle_use_deepest_state - Enable/disable the "deepest idle" mode.
- * @enable: Whether enable or disable the feature.
- *
- * If the "deepest idle" mode is enabled, cpuidle will ignore the governor and
- * always use the state with the greatest exit latency (out of the states that
- * are not disabled).
- *
- * This function can only be called after cpuidle_pause() to avoid races.
- */
-void cpuidle_use_deepest_state(bool enable)
-{
-	use_deepest_state = enable;
-}
-
-/**
- * cpuidle_find_deepest_state - Find the state of the greatest exit latency.
- * @drv: cpuidle driver for a given CPU.
- * @dev: cpuidle device for a given CPU.
+ * cpuidle_find_deepest_state - Find deepest state meeting specific conditions.
+ * @drv: cpuidle driver for the given CPU.
+ * @dev: cpuidle device for the given CPU.
+ * @freeze: Whether or not the state should be suitable for suspend-to-idle.
  */
 static int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
-				      struct cpuidle_device *dev)
+				      struct cpuidle_device *dev, bool freeze)
 {
 	unsigned int latency_req = 0;
-	int i, ret = CPUIDLE_DRIVER_STATE_START - 1;
+	int i, ret = freeze ? -1 : CPUIDLE_DRIVER_STATE_START - 1;
 
 	for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
 		struct cpuidle_state *s = &drv->states[i];
 		struct cpuidle_state_usage *su = &dev->states_usage[i];
 
-		if (s->disabled || su->disable || s->exit_latency <= latency_req)
+		if (s->disabled || su->disable || s->exit_latency <= latency_req
+		    || (freeze && !s->enter_freeze))
 			continue;
 
 		latency_req = s->exit_latency;
@@ -104,6 +92,63 @@ static int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
 	return ret;
 }
 
+static void enter_freeze_proper(struct cpuidle_driver *drv,
+				struct cpuidle_device *dev, int index)
+{
+	tick_freeze();
+	/*
+	 * The state used here cannot be a "coupled" one, because the "coupled"
+	 * cpuidle mechanism enables interrupts and doing that with timekeeping
+	 * suspended is generally unsafe.
+	 */
+	drv->states[index].enter_freeze(dev, drv, index);
+	WARN_ON(!irqs_disabled());
+	/*
+	 * timekeeping_resume() that will be called by tick_unfreeze() for the
+	 * last CPU executing it calls functions containing RCU read-side
+	 * critical sections, so tell RCU about that.
+	 */
+	RCU_NONIDLE(tick_unfreeze());
+}
+
+/**
+ * cpuidle_enter_freeze - Enter an idle state suitable for suspend-to-idle.
+ *
+ * If there are states with the ->enter_freeze callback, find the deepest of
+ * them and enter it with frozen tick.  Otherwise, find the deepest state
+ * available and enter it normally.
+ */
+void cpuidle_enter_freeze(void)
+{
+	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
+	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
+	int index;
+
+	/*
+	 * Find the deepest state with ->enter_freeze present, which guarantees
+	 * that interrupts won't be enabled when it exits and allows the tick to
+	 * be frozen safely.
+	 */
+	index = cpuidle_find_deepest_state(drv, dev, true);
+	if (index >= 0) {
+		enter_freeze_proper(drv, dev, index);
+		return;
+	}
+
+	/*
+	 * It is not safe to freeze the tick, find the deepest state available
+	 * at all and try to enter it normally.
+	 */
+	index = cpuidle_find_deepest_state(drv, dev, false);
+	if (index >= 0)
+		cpuidle_enter(drv, dev, index);
+	else
+		arch_cpu_idle();
+
+	/* Interrupts are enabled again here. */
+	local_irq_disable();
+}
+
 /**
  * cpuidle_enter_state - enter the state and update stats
  * @dev: cpuidle device for this cpu
@@ -166,9 +211,6 @@ int cpuidle_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	if (!drv || !dev || !dev->enabled)
 		return -EBUSY;
 
-	if (unlikely(use_deepest_state))
-		return cpuidle_find_deepest_state(drv, dev);
-
 	return cpuidle_curr_governor->select(drv, dev);
 }
 
@@ -200,7 +242,7 @@ int cpuidle_enter(struct cpuidle_driver *drv, struct cpuidle_device *dev,
  */
 void cpuidle_reflect(struct cpuidle_device *dev, int index)
 {
-	if (cpuidle_curr_governor->reflect && !unlikely(use_deepest_state))
+	if (cpuidle_curr_governor->reflect)
 		cpuidle_curr_governor->reflect(dev, index);
 }