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>

5 files changed, 250 insertions, 19 deletions

diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index deb5461e321..67947083f84 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 66d808ec525..010b2f7e148 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 00000000000..42348e3589d
--- /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;
+        }
+
+        if (autosleep_state == PM_SUSPEND_ON) {
+                mutex_unlock(&autosleep_lock);
+                return;
+        }
+        if (autosleep_state >= PM_SUSPEND_MAX)
+                hibernate();
+        else
+                pm_suspend(autosleep_state);
+
+        mutex_unlock(&autosleep_lock);
+
+        if (!pm_get_wakeup_count(&final_count, false))
+                goto out;
+
+        /*
+         * If the wakeup occured for an unknown reason, wait to prevent the
+         * system from trying to suspend and waking up in a tight loop.
+         */
+        if (final_count == initial_count)
+                schedule_timeout_uninterruptible(HZ / 2);
+
+ out:
+        queue_up_suspend_work();
+}
+
+static DECLARE_WORK(suspend_work, try_to_suspend);
+
+void queue_up_suspend_work(void)
+{
+        if (!work_pending(&suspend_work) && autosleep_state > PM_SUSPEND_ON)
+                queue_work(autosleep_wq, &suspend_work);
+}
+
+suspend_state_t pm_autosleep_state(void)
+{
+        return autosleep_state;
+}
+
+int pm_autosleep_lock(void)
+{
+        return mutex_lock_interruptible(&autosleep_lock);
+}
+
+void pm_autosleep_unlock(void)
+{
+        mutex_unlock(&autosleep_lock);
+}
+
+int pm_autosleep_set_state(suspend_state_t state)
+{
+
+#ifndef CONFIG_HIBERNATION
+        if (state >= PM_SUSPEND_MAX)
+                return -EINVAL;
+#endif
+
+        __pm_stay_awake(autosleep_ws);
+
+        mutex_lock(&autosleep_lock);
+
+        autosleep_state = state;
+
+        __pm_relax(autosleep_ws);
+
+        if (state > PM_SUSPEND_ON)
+                queue_up_suspend_work();
+
+        mutex_unlock(&autosleep_lock);
+        return 0;
+}
+
+int __init pm_autosleep_init(void)
+{
+        autosleep_ws = wakeup_source_register("autosleep");
+        if (!autosleep_ws)
+                return -ENOMEM;
+
+        autosleep_wq = alloc_ordered_workqueue("autosleep", 0);
+        if (autosleep_wq)
+                return 0;
+
+        wakeup_source_unregister(autosleep_ws);
+        return -ENOMEM;
+}
diff --git a/kernel/power/main.c b/kernel/power/main.c
index 1c12581f1c6..ba6a5645952 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -269,8 +269,7 @@ static ssize_t state_show(struct kobject *kobj, struct kobj_attribute *attr,
         return (s - buf);
 }
 
-static ssize_t state_store(struct kobject *kobj, struct kobj_attribute *attr,
-                           const char *buf, size_t n)
+static suspend_state_t decode_state(const char *buf, size_t n)
 {
 #ifdef CONFIG_SUSPEND
         suspend_state_t state = PM_SUSPEND_STANDBY;
@@ -278,27 +277,48 @@ static ssize_t state_store(struct kobject *kobj, struct kobj_attribute *attr,
 #endif
         char *p;
         int len;
-        int error = -EINVAL;
 
         p = memchr(buf, '\n', n);
         len = p ? p - buf : n;
 
-        /* First, check if we are requested to hibernate */
-        if (len == 4 && !strncmp(buf, "disk", len)) {
-                error = hibernate();
-                goto Exit;
-        }
+        /* Check hibernation first. */
+        if (len == 4 && !strncmp(buf, "disk", len))
+                return PM_SUSPEND_MAX;
 
 #ifdef CONFIG_SUSPEND
-        for (s = &pm_states[state]; state < PM_SUSPEND_MAX; s++, state++) {
-                if (*s && len == strlen(*s) && !strncmp(buf, *s, len)) {
-                        error = pm_suspend(state);
-                        break;
-                }
-        }
+        for (s = &pm_states[state]; state < PM_SUSPEND_MAX; s++, state++)
+                if (*s && len == strlen(*s) && !strncmp(buf, *s, len))
+                        return state;
 #endif
 
- Exit:
+        return PM_SUSPEND_ON;
+}
+
+static ssize_t state_store(struct kobject *kobj, struct kobj_attribute *attr,
+                           const char *buf, size_t n)
+{
+        suspend_state_t state;
+        int error;
+
+        error = pm_autosleep_lock();
+        if (error)
+                return error;
+
+        if (pm_autosleep_state() > PM_SUSPEND_ON) {
+                error = -EBUSY;
+                goto out;
+        }
+
+        state = decode_state(buf, n);
+        if (state < PM_SUSPEND_MAX)
+                error = pm_suspend(state);
+        else if (state == PM_SUSPEND_MAX)
+                error = hibernate();
+        else
+                error = -EINVAL;
+
+ out:
+        pm_autosleep_unlock();
         return error ? error : n;
 }
 
@@ -339,7 +359,8 @@ static ssize_t wakeup_count_show(struct kobject *kobj,
 {
         unsigned int val;
 
-        return pm_get_wakeup_count(&val) ? sprintf(buf, "%u\n", val) : -EINTR;
+        return pm_get_wakeup_count(&val, true) ?
+                sprintf(buf, "%u\n", val) : -EINTR;
 }
 
 static ssize_t wakeup_count_store(struct kobject *kobj,
@@ -347,15 +368,69 @@ static ssize_t wakeup_count_store(struct kobject *kobj,
                                 const char *buf, size_t n)
 {
         unsigned int val;
+        int error;
+
+        error = pm_autosleep_lock();
+        if (error)
+                return error;
 
+        if (pm_autosleep_state() > PM_SUSPEND_ON) {
+                error = -EBUSY;
+                goto out;
+        }
+
+        error = -EINVAL;
         if (sscanf(buf, "%u", &val) == 1) {
                 if (pm_save_wakeup_count(val))
-                        return n;
+                        error = n;
         }
-        return -EINVAL;
+
+ out:
+        pm_autosleep_unlock();
+        return error;
 }
 
 power_attr(wakeup_count);
+
+#ifdef CONFIG_PM_AUTOSLEEP
+static ssize_t autosleep_show(struct kobject *kobj,
+                              struct kobj_attribute *attr,
+                              char *buf)
+{
+        suspend_state_t state = pm_autosleep_state();
+
+        if (state == PM_SUSPEND_ON)
+                return sprintf(buf, "off\n");
+
+#ifdef CONFIG_SUSPEND
+        if (state < PM_SUSPEND_MAX)
+                return sprintf(buf, "%s\n", valid_state(state) ?
+                                                pm_states[state] : "error");
+#endif
+#ifdef CONFIG_HIBERNATION
+        return sprintf(buf, "disk\n");
+#else
+        return sprintf(buf, "error");
+#endif
+}
+
+static ssize_t autosleep_store(struct kobject *kobj,
+                               struct kobj_attribute *attr,
+                               const char *buf, size_t n)
+{
+        suspend_state_t state = decode_state(buf, n);
+        int error;
+
+        if (state == PM_SUSPEND_ON
+            && !(strncmp(buf, "off", 3) && strncmp(buf, "off\n", 4)))
+                return -EINVAL;
+
+        error = pm_autosleep_set_state(state);
+        return error ? error : n;
+}
+
+power_attr(autosleep);
+#endif /* CONFIG_PM_AUTOSLEEP */
 #endif /* CONFIG_PM_SLEEP */
 
 #ifdef CONFIG_PM_TRACE
@@ -409,6 +484,9 @@ static struct attribute * g[] = {
 #ifdef CONFIG_PM_SLEEP
         &pm_async_attr.attr,
         &wakeup_count_attr.attr,
+#ifdef CONFIG_PM_AUTOSLEEP
+        &autosleep_attr.attr,
+#endif
 #ifdef CONFIG_PM_DEBUG
         &pm_test_attr.attr,
 #endif
@@ -444,7 +522,10 @@ static int __init pm_init(void)
         power_kobj = kobject_create_and_add("power", NULL);
         if (!power_kobj)
                 return -ENOMEM;
-        return sysfs_create_group(power_kobj, &attr_group);
+        error = sysfs_create_group(power_kobj, &attr_group);
+        if (error)
+                return error;
+        return pm_autosleep_init();
 }
 
 core_initcall(pm_init);
diff --git a/kernel/power/power.h b/kernel/power/power.h
index 98f3622d740..4cf80fa115d 100644
--- a/kernel/power/power.h
+++ b/kernel/power/power.h
@@ -264,3 +264,21 @@ static inline void suspend_thaw_processes(void)
 {
 }
 #endif
+
+#ifdef CONFIG_PM_AUTOSLEEP
+
+/* kernel/power/autosleep.c */
+extern int pm_autosleep_init(void);
+extern int pm_autosleep_lock(void);
+extern void pm_autosleep_unlock(void);
+extern suspend_state_t pm_autosleep_state(void);
+extern int pm_autosleep_set_state(suspend_state_t state);
+
+#else /* !CONFIG_PM_AUTOSLEEP */
+
+static inline int pm_autosleep_init(void) { return 0; }
+static inline int pm_autosleep_lock(void) { return 0; }
+static inline void pm_autosleep_unlock(void) {}
+static inline suspend_state_t pm_autosleep_state(void) { return PM_SUSPEND_ON; }
+
+#endif /* !CONFIG_PM_AUTOSLEEP */