[PATCH 8] PM: Allow user space to change the power.async_suspend flag of devices

["Rafael J. Wysocki" <rjw@sisk.pl>]

From: Rafael J. Wysocki <rjw@sisk.pl>

Add sysfs attribute power/async for every device allowing the user
space to access the device's power.async_suspend flag and modify it,
if necessary.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
 drivers/base/power/sysfs.c |   47 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/device.h     |    5 ++++
 2 files changed, 52 insertions(+)

Index: linux-2.6/drivers/base/power/sysfs.c
===================================================================
--- linux-2.6.orig/drivers/base/power/sysfs.c
+++ linux-2.6/drivers/base/power/sysfs.c
@@ -38,6 +38,22 @@
  *	wakeup events internally (unless they are disabled), keeping
  *	their hardware in low power modes whenever they're unused.  This
  *	saves runtime power, without requiring system-wide sleep states.
+ *
+ *	async - Report/change current async suspend setting for the device
+ *
+ *	If set, the PM core will attempt to suspend and resume the device during
+ *	system power transitions (e.g. suspend to RAM, hibernation) in parallel
+ *	with other devices it doesn't appear to depend on (to the PM core's
+ *	knowledge).
+ *
+ *	 + "enabled\n" to permit the asynchronous suspend/resume of the device
+ *	 + "disabled\n" to forbid it
+ *
+ *	NOTE: It generally is unsafe to permit the asynchronous suspend/resume
+ *	of a device unless it is certain that all of the PM dependencies of the
+ *	device are known to the PM core.  However, for some devices this
+ *	attribute is set to "enabled" by the kernel and in that cases it should
+ *	be safe to leave the default value.
  */
 
 static const char enabled[] = "enabled";
@@ -77,9 +93,40 @@ wake_store(struct device * dev, struct d
 
 static DEVICE_ATTR(wakeup, 0644, wake_show, wake_store);
 
+#ifdef CONFIG_PM_SLEEP
+static ssize_t async_show(struct device *dev, struct device_attribute *attr,
+			  char *buf)
+{
+	return sprintf(buf, "%s\n",
+			device_async_suspend_enabled(dev) ? enabled : disabled);
+}
+
+static ssize_t async_store(struct device *dev, struct device_attribute *attr,
+			   const char *buf, size_t n)
+{
+	char *cp;
+	int len = n;
+
+	cp = memchr(buf, '\n', n);
+	if (cp)
+		len = cp - buf;
+	if (len == sizeof enabled - 1 && strncmp(buf, enabled, len) == 0)
+		device_enable_async_suspend(dev, true);
+	else if (len == sizeof disabled - 1 && strncmp(buf, disabled, len) == 0)
+		device_enable_async_suspend(dev, false);
+	else
+		return -EINVAL;
+	return n;
+}
+
+static DEVICE_ATTR(async, 0644, async_show, async_store);
+#endif /* CONFIG_PM_SLEEP */
 
 static struct attribute * power_attrs[] = {
 	&dev_attr_wakeup.attr,
+#ifdef CONFIG_PM_SLEEP
+	&dev_attr_async.attr,
+#endif
 	NULL,
 };
 static struct attribute_group pm_attr_group = {
Index: linux-2.6/include/linux/device.h
===================================================================
--- linux-2.6.orig/include/linux/device.h
+++ linux-2.6/include/linux/device.h
@@ -478,6 +478,11 @@ static inline void device_enable_async_s
 		dev->power.async_suspend = enable;
 }
 
+static inline bool device_async_suspend_enabled(struct device *dev)
+{
+	return !!dev->power.async_suspend;
+}
+
 void driver_init(void);
 
 /*