PM / sleep: Re-implement suspend-to-idle handling

In preparation for adding support for quiescing timers in the final
stage of suspend-to-idle transitions, rework the freeze_enter()
function making the system wait on a wakeup event, the freeze_wake()
function terminating the suspend-to-idle loop and the mechanism by
which deep idle states are entered during suspend-to-idle.

First of all, introduce a simple state machine for suspend-to-idle
and make the code in question use it.

Second, prevent freeze_enter() from losing wakeup events due to race
conditions and ensure that the number of online CPUs won't change
while it is being executed.  In addition to that, make it force
all of the CPUs re-enter the idle loop in case they are in idle
states already (so they can enter deeper idle states if possible).

Next, drop cpuidle_use_deepest_state() and replace use_deepest_state
checks in cpuidle_select() and cpuidle_reflect() with a single
suspend-to-idle state check in cpuidle_idle_call().

Finally, introduce cpuidle_enter_freeze() that will simply find the
deepest idle state available to the given CPU and enter it using
cpuidle_enter().

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index 3388c1b6f7d8..5efe743ce1e8 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -201,6 +201,21 @@ struct platform_freeze_ops {
  */
 extern void suspend_set_ops(const struct platform_suspend_ops *ops);
 extern int suspend_valid_only_mem(suspend_state_t state);
+
+/* Suspend-to-idle state machnine. */
+enum freeze_state {
+	FREEZE_STATE_NONE,      /* Not suspended/suspending. */
+	FREEZE_STATE_ENTER,     /* Enter suspend-to-idle. */
+	FREEZE_STATE_WAKE,      /* Wake up from suspend-to-idle. */
+};
+
+extern enum freeze_state __read_mostly suspend_freeze_state;
+
+static inline bool idle_should_freeze(void)
+{
+	return unlikely(suspend_freeze_state == FREEZE_STATE_ENTER);
+}
+
 extern void freeze_set_ops(const struct platform_freeze_ops *ops);
 extern void freeze_wake(void);
 
@@ -228,6 +243,7 @@ extern int pm_suspend(suspend_state_t state);
 
 static inline void suspend_set_ops(const struct platform_suspend_ops *ops) {}
 static inline int pm_suspend(suspend_state_t state) { return -ENOSYS; }
+static inline bool idle_should_freeze(void) { return false; }
 static inline void freeze_set_ops(const struct platform_freeze_ops *ops) {}
 static inline void freeze_wake(void) {}
 #endif /* !CONFIG_SUSPEND */