4 files changed, 50 insertions, 7 deletions

diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
index dcff4d0623ad..d6a801f45b48 100644
--- a/Documentation/ABI/testing/sysfs-power
+++ b/Documentation/ABI/testing/sysfs-power
@@ -101,3 +101,16 @@ Description:
 
                 CAUTION: Using it will cause your machine's real-time (CMOS)
                 clock to be set to a random invalid time after a resume.
+
+What:           /sys/power/pm_async
+Date:           January 2009
+Contact:        Rafael J. Wysocki <rjw@sisk.pl>
+Description:
+                The /sys/power/pm_async file controls the switch allowing the
+                user space to enable or disable asynchronous suspend and resume
+                of devices.  If enabled, this feature will cause some device
+                drivers' suspend and resume callbacks to be executed in parallel
+                with each other and with the main suspend thread.  It is enabled
+                if this file contains "1", which is the default.  It may be
+                disabled by writing "0" to this file, in which case all devices
+                will be suspended and resumed synchronously.
diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 3b44c201ddad..7e79201b09bb 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -201,7 +201,7 @@ static void dpm_wait(struct device *dev, bool async)
         if (!dev)
                 return;
 
-        if (async || dev->power.async_suspend)
+        if (async || (pm_async_enabled && dev->power.async_suspend))
                 wait_for_completion(&dev->power.completion);
 }
 
@@ -563,7 +563,8 @@ static int device_resume(struct device *dev)
 {
         INIT_COMPLETION(dev->power.completion);
 
-        if (dev->power.async_suspend && !pm_trace_is_enabled()) {
+        if (pm_async_enabled && dev->power.async_suspend
+            && !pm_trace_is_enabled()) {
                 get_device(dev);
                 async_schedule(async_resume, dev);
                 return 0;
@@ -867,7 +868,7 @@ static int device_suspend(struct device *dev)
 {
         INIT_COMPLETION(dev->power.completion);
 
-        if (dev->power.async_suspend) {
+        if (pm_async_enabled && dev->power.async_suspend) {
                 get_device(dev);
                 async_schedule(async_suspend, dev);
                 return 0;
diff --git a/drivers/base/power/power.h b/drivers/base/power/power.h
index b8fa1aa5225a..c0bd03c83b9c 100644
--- a/drivers/base/power/power.h
+++ b/drivers/base/power/power.h
@@ -12,10 +12,10 @@ static inline void pm_runtime_remove(struct device *dev) {}
 
 #ifdef CONFIG_PM_SLEEP
 
-/*
- * main.c
- */
+/* kernel/power/main.c */
+extern int pm_async_enabled;
 
+/* drivers/base/power/main.c */
 extern struct list_head dpm_list;       /* The active device list */
 
 static inline struct device *to_device(struct list_head *entry)
diff --git a/kernel/power/main.c b/kernel/power/main.c
index 0998c7139053..b58800b21fc0 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -44,6 +44,32 @@ int pm_notifier_call_chain(unsigned long val)
                         == NOTIFY_BAD) ? -EINVAL : 0;
 }
 
+/* If set, devices may be suspended and resumed asynchronously. */
+int pm_async_enabled = 1;
+
+static ssize_t pm_async_show(struct kobject *kobj, struct kobj_attribute *attr,
+                             char *buf)
+{
+        return sprintf(buf, "%d\n", pm_async_enabled);
+}
+
+static ssize_t pm_async_store(struct kobject *kobj, struct kobj_attribute *attr,
+                              const char *buf, size_t n)
+{
+        unsigned long val;
+
+        if (strict_strtoul(buf, 10, &val))
+                return -EINVAL;
+
+        if (val > 1)
+                return -EINVAL;
+
+        pm_async_enabled = val;
+        return n;
+}
+
+power_attr(pm_async);
+
 #ifdef CONFIG_PM_DEBUG
 int pm_test_level = TEST_NONE;
 
@@ -208,9 +234,12 @@ static struct attribute * g[] = {
 #ifdef CONFIG_PM_TRACE
         &pm_trace_attr.attr,
 #endif
-#if defined(CONFIG_PM_SLEEP) && defined(CONFIG_PM_DEBUG)
+#ifdef CONFIG_PM_SLEEP
+        &pm_async_attr.attr,
+#ifdef CONFIG_PM_DEBUG
         &pm_test_attr.attr,
 #endif
+#endif
         NULL,
 };