PM: Add a switch for disabling/enabling asynchronous suspend/resume

Add sysfs attribute /sys/power/pm_async allowing the user space to
disable/enable asynchronous suspend/resume of devices.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

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.

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;

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)

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;
 
@@ -208,8 +234,11 @@ 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,
 };