PM / Sleep: Implement opportunistic sleep, v2

Introduce a mechanism by which the kernel can trigger global
transitions to a sleep state chosen by user space if there are no
active wakeup sources.

It consists of a new sysfs attribute, /sys/power/autosleep, that
can be written one of the strings returned by reads from
/sys/power/state, an ordered workqueue and a work item carrying out
the "suspend" operations.  If a string representing the system's
sleep state is written to /sys/power/autosleep, the work item
triggering transitions to that state is queued up and it requeues
itself after every execution until user space writes "off" to
/sys/power/autosleep.

That work item enables the detection of wakeup events using the
functions already defined in drivers/base/power/wakeup.c (with one
small modification) and calls either pm_suspend(), or hibernate() to
put the system into a sleep state.  If a wakeup event is reported
while the transition is in progress, it will abort the transition and
the "system suspend" work item will be queued up again.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: NeilBrown <neilb@suse.de>

8 files changed, 298 insertions, 35 deletions

diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
index b464d12761ba..237c735db6c9 100644
--- a/Documentation/ABI/testing/sysfs-power
+++ b/Documentation/ABI/testing/sysfs-power
@@ -172,3 +172,20 @@ Description:
 
                 Reading from this file will display the current value, which is
                 set to 1 MB by default.
+
+What:           /sys/power/autosleep
+Date:           April 2012
+Contact:        Rafael J. Wysocki <rjw@sisk.pl>
+Description:
+                The /sys/power/autosleep file can be written one of the strings
+                returned by reads from /sys/power/state.  If that happens, a
+                work item attempting to trigger a transition of the system to
+                the sleep state represented by that string is queued up.  This
+                attempt will only succeed if there are no active wakeup sources
+                in the system at that time.  After every execution, regardless
+                of whether or not the attempt to put the system to sleep has
+                succeeded, the work item requeues itself until user space
+                writes "off" to /sys/power/autosleep.
+
+                Reading from this file causes the last string successfully
+                written to it to be returned.
diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
index 1132799421cd..cf1706df7610 100644
--- a/drivers/base/power/wakeup.c
+++ b/drivers/base/power/wakeup.c
@@ -660,29 +660,33 @@ bool pm_wakeup_pending(void)
 /**
  * pm_get_wakeup_count - Read the number of registered wakeup events.
  * @count: Address to store the value at.
+ * @block: Whether or not to block.
  *
- * Store the number of registered wakeup events at the address in @count.  Block
- * if the current number of wakeup events being processed is nonzero.
+ * Store the number of registered wakeup events at the address in @count.  If
+ * @block is set, block until the current number of wakeup events being
+ * processed is zero.
  *
- * Return 'false' if the wait for the number of wakeup events being processed to
- * drop down to zero has been interrupted by a signal (and the current number
- * of wakeup events being processed is still nonzero).  Otherwise return 'true'.
+ * Return 'false' if the current number of wakeup events being processed is
+ * nonzero.  Otherwise return 'true'.
  */
-bool pm_get_wakeup_count(unsigned int *count)
+bool pm_get_wakeup_count(unsigned int *count, bool block)
 {
         unsigned int cnt, inpr;
-        DEFINE_WAIT(wait);
 
-        for (;;) {
-                prepare_to_wait(&wakeup_count_wait_queue, &wait,
-                                TASK_INTERRUPTIBLE);
-                split_counters(&cnt, &inpr);
-                if (inpr == 0 || signal_pending(current))
-                        break;
+        if (block) {
+                DEFINE_WAIT(wait);
+
+                for (;;) {
+                        prepare_to_wait(&wakeup_count_wait_queue, &wait,
+                                        TASK_INTERRUPTIBLE);
+                        split_counters(&cnt, &inpr);
+                        if (inpr == 0 || signal_pending(current))
+                                break;
 
-                schedule();
+                        schedule();
+                }
+                finish_wait(&wakeup_count_wait_queue, &wait);
         }
-        finish_wait(&wakeup_count_wait_queue, &wait);
 
         split_counters(&cnt, &inpr);
         *count = cnt;
diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index ac1c114c499d..76b7ec7d3a81 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -356,7 +356,7 @@ extern int unregister_pm_notifier(struct notifier_block *nb);
 extern bool events_check_enabled;
 
 extern bool pm_wakeup_pending(void);
-extern bool pm_get_wakeup_count(unsigned int *count);
+extern bool pm_get_wakeup_count(unsigned int *count, bool block);
 extern bool pm_save_wakeup_count(unsigned int count);
 
 static inline void lock_system_sleep(void)
@@ -407,6 +407,17 @@ static inline void unlock_system_sleep(void) {}
 
 #endif /* !CONFIG_PM_SLEEP */
 
+#ifdef CONFIG_PM_AUTOSLEEP
+
+/* kernel/power/autosleep.c */
+void queue_up_suspend_work(void);
+
+#else /* !CONFIG_PM_AUTOSLEEP */
+
+static inline void queue_up_suspend_work(void) {}
+
+#endif /* !CONFIG_PM_AUTOSLEEP */
+
 #ifdef CONFIG_ARCH_SAVE_PAGE_KEYS
 /*
  * The ARCH_SAVE_PAGE_KEYS functions can be used by an architecture
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index deb5461e3216..67947083f842 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -103,6 +103,14 @@ config PM_SLEEP_SMP
         select HOTPLUG
         select HOTPLUG_CPU
 
+config PM_AUTOSLEEP
+        bool "Opportunistic sleep"
+        depends on PM_SLEEP
+        default n
+        ---help---
+        Allow the kernel to trigger a system transition into a global sleep
+        state automatically whenever there are no active wakeup sources.
+
 config PM_RUNTIME
         bool "Run-time PM core functionality"
         depends on !IA64_HP_SIM
diff --git a/kernel/power/Makefile b/kernel/power/Makefile
index 66d808ec5252..010b2f7e148c 100644
--- a/kernel/power/Makefile
+++ b/kernel/power/Makefile
@@ -9,5 +9,6 @@ obj-$(CONFIG_SUSPEND)		+= suspend.o
 obj-$(CONFIG_PM_TEST_SUSPEND)   += suspend_test.o
 obj-$(CONFIG_HIBERNATION)       += hibernate.o snapshot.o swap.o user.o \
                                    block_io.o
+obj-$(CONFIG_PM_AUTOSLEEP)      += autosleep.o
 
 obj-$(CONFIG_MAGIC_SYSRQ)       += poweroff.o
diff --git a/kernel/power/autosleep.c b/kernel/power/autosleep.c
new file mode 100644
index 000000000000..42348e3589d3
--- /dev/null
+++ b/kernel/power/autosleep.c
@@ -0,0 +1,123 @@
+/*
+ * kernel/power/autosleep.c
+ *
+ * Opportunistic sleep support.
+ *
+ * Copyright (C) 2012 Rafael J. Wysocki <rjw@sisk.pl>
+ */
+
+#include <linux/device.h>
+#include <linux/mutex.h>
+#include <linux/pm_wakeup.h>
+
+#include "power.h"
+
+static suspend_state_t autosleep_state;
+static struct workqueue_struct *autosleep_wq;
+/*
+ * Note: it is only safe to mutex_lock(&autosleep_lock) if a wakeup_source
+ * is active, otherwise a deadlock with try_to_suspend() is possible.
+ * Alternatively mutex_lock_interruptible() can be used.  This will then fail
+ * if an auto_sleep cycle tries to freeze processes.
+ */
+static DEFINE_MUTEX(autosleep_lock);
+static struct wakeup_source *autosleep_ws;
+
+static void try_to_suspend(struct work_struct *work)
+{
+        unsigned int initial_count, final_count;
+
+        if (!pm_get_wakeup_count(&initial_count, true))
+                goto out;
+
+        mutex_lock(&autosleep_lock);
+
+        if (!pm_save_wakeup_count(initial_count)) {
+                mutex_unlock(&autosleep_lock);
+                goto out;
+        }
+