PM: Do not create wakeup sysfs files for devices that cannot wake up

Currently, wakeup sysfs attributes are created for all devices,
regardless of whether or not they are wakeup-capable. This is
excessive and complicates wakeup device identification from user
space (i.e. to identify wakeup-capable devices user space has to read
/sys/devices/.../power/wakeup for all devices and see if they are not
empty).

Fix this issue by avoiding to create wakeup sysfs files for devices
that cannot wake up the system from sleep states (i.e. whose
power.can_wakeup flags are unset during registration) and modify
device_set_wakeup_capable() so that it adds (or removes) the relevant
sysfs attributes if a device's wakeup capability status is changed.

Signed-off-by: Rafael J. Wysocki <[e-mail]>

Documentation/ABI/testing/sysfs-devices-power

···
 		"disabled" to it.
 
 		For the devices that are not capable of generating system wakeup
-		events this file contains "\n".  In that cases the user space
-		cannot modify the contents of this file and the device cannot be
-		enabled to wake up the system.
+		events this file is not present.  In that case the device cannot
+		be enabled to wake up the system from sleep states.
 
 What:		/sys/devices/.../power/control
 Date:		January 2009
···
 		The /sys/devices/.../wakeup_count attribute contains the number
 		of signaled wakeup events associated with the device.  This
 		attribute is read-only.  If the device is not enabled to wake up
-		the system from sleep states, this attribute is empty.
+		the system from sleep states, this attribute is not present.
 
 What:		/sys/devices/.../power/wakeup_active_count
 Date:		September 2010
···
 		number of times the processing of wakeup events associated with
 		the device was completed (at the kernel level).  This attribute
 		is read-only.  If the device is not enabled to wake up the
-		system from sleep states, this attribute is empty.
+		system from sleep states, this attribute is not present.
 
 What:		/sys/devices/.../power/wakeup_hit_count
 Date:		September 2010
···
 		number of times the processing of a wakeup event associated with
 		the device might prevent the system from entering a sleep state.
 		This attribute is read-only.  If the device is not enabled to
-		wake up the system from sleep states, this attribute is empty.
+		wake up the system from sleep states, this attribute is not
+		present.
 
 What:		/sys/devices/.../power/wakeup_active
 Date:		September 2010
···
 		or 0, depending on whether or not a wakeup event associated with
 		the device is being processed (1).  This attribute is read-only.
 		If the device is not enabled to wake up the system from sleep
-		states, this attribute is empty.
+		states, this attribute is not present.
 
 What:		/sys/devices/.../power/wakeup_total_time_ms
 Date:		September 2010
···
 		the total time of processing wakeup events associated with the
 		device, in milliseconds.  This attribute is read-only.  If the
 		device is not enabled to wake up the system from sleep states,
-		this attribute is empty.
+		this attribute is not present.
 
 What:		/sys/devices/.../power/wakeup_max_time_ms
 Date:		September 2010
···
 		the maximum time of processing a single wakeup event associated
 		with the device, in milliseconds.  This attribute is read-only.
 		If the device is not enabled to wake up the system from sleep
-		states, this attribute is empty.
+		states, this attribute is not present.
 
 What:		/sys/devices/.../power/wakeup_last_time_ms
 Date:		September 2010
···
 		signaling the last wakeup event associated with the device, in
 		milliseconds.  This attribute is read-only.  If the device is
 		not enabled to wake up the system from sleep states, this
-		attribute is empty.
+		attribute is not present.
 
 What:		/sys/devices/.../power/autosuspend_delay_ms
 Date:		September 2010

Documentation/power/devices.txt

···
 whether or not a wakeup-capable device should issue wakeup events is a policy
 decision, and it is managed by user space through a sysfs attribute: the
 power/wakeup file.  User space can write the strings "enabled" or "disabled" to
-set or clear the should_wakeup flag, respectively.  Reads from the file will
-return the corresponding string if can_wakeup is true, but if can_wakeup is
-false then reads will return an empty string, to indicate that the device
-doesn't support wakeup events.  (But even though the file appears empty, writes
-will still affect the should_wakeup flag.)
+set or clear the "should_wakeup" flag, respectively.  This file is only present
+for wakeup-capable devices (i.e. devices whose "can_wakeup" flags are set)
+and is created (or removed) by device_set_wakeup_capable().  Reads from the
+file will return the corresponding string.
 
 The device_may_wakeup() routine returns true only if both flags are set.
-Drivers should check this routine when putting devices in a low-power state
-during a system sleep transition, to see whether or not to enable the devices'
-wakeup mechanisms.  However for runtime power management, wakeup events should
-be enabled whenever the device and driver both support them, regardless of the
-should_wakeup flag.
+This information is used by subsystems, like the PCI bus type code, to see
+whether or not to enable the devices' wakeup mechanisms.  If device wakeup
+mechanisms are enabled or disabled directly by drivers, they also should use
+device_may_wakeup() to decide what to do during a system sleep transition.
+However for runtime power management, wakeup events should be enabled whenever
+the device and driver both support them, regardless of the should_wakeup flag.
 
 
 /sys/devices/.../power/control files

drivers/base/power/power.h

···
  * sysfs.c
  */
 
-extern int dpm_sysfs_add(struct device *);
-extern void dpm_sysfs_remove(struct device *);
-extern void rpm_sysfs_remove(struct device *);
+extern int dpm_sysfs_add(struct device *dev);
+extern void dpm_sysfs_remove(struct device *dev);
+extern void rpm_sysfs_remove(struct device *dev);
+extern int wakeup_sysfs_add(struct device *dev);
+extern void wakeup_sysfs_remove(struct device *dev);
 
 #else /* CONFIG_PM */
 
-static inline int dpm_sysfs_add(struct device *dev)
-{
-	return 0;
-}
-
-static inline void dpm_sysfs_remove(struct device *dev)
-{
-}
+static inline int dpm_sysfs_add(struct device *dev) { return 0; }
+static inline void dpm_sysfs_remove(struct device *dev) {}
+static inline void rpm_sysfs_remove(struct device *dev) {}
+static inline int wakeup_sysfs_add(struct device *dev) { return 0; }
+static inline void wakeup_sysfs_remove(struct device *dev) {}
 
 #endif

drivers/base/power/sysfs.c

···
 static DEVICE_ATTR(async, 0644, async_show, async_store);
 #endif /* CONFIG_PM_ADVANCED_DEBUG */
 
-static struct attribute * power_attrs[] = {
-	&dev_attr_wakeup.attr,
+static struct attribute *power_attrs[] = {
+#ifdef CONFIG_PM_ADVANCED_DEBUG
 #ifdef CONFIG_PM_SLEEP
+	&dev_attr_async.attr,
+#endif
+#ifdef CONFIG_PM_RUNTIME
+	&dev_attr_runtime_status.attr,
+	&dev_attr_runtime_usage.attr,
+	&dev_attr_runtime_active_kids.attr,
+	&dev_attr_runtime_enabled.attr,
+#endif
+#endif /* CONFIG_PM_ADVANCED_DEBUG */
+	NULL,
+};
+static struct attribute_group pm_attr_group = {
+	.name	= power_group_name,
+	.attrs	= power_attrs,
+};
+
+static struct attribute *wakeup_attrs[] = {
+#ifdef CONFIG_PM_SLEEP
+	&dev_attr_wakeup.attr,
 	&dev_attr_wakeup_count.attr,
 	&dev_attr_wakeup_active_count.attr,
 	&dev_attr_wakeup_hit_count.attr,
···
 	&dev_attr_wakeup_max_time_ms.attr,
 	&dev_attr_wakeup_last_time_ms.attr,
 #endif
-#ifdef CONFIG_PM_ADVANCED_DEBUG
-	&dev_attr_async.attr,
-#ifdef CONFIG_PM_RUNTIME
-	&dev_attr_runtime_status.attr,
-	&dev_attr_runtime_usage.attr,
-	&dev_attr_runtime_active_kids.attr,
-	&dev_attr_runtime_enabled.attr,
-#endif
-#endif
 	NULL,
 };
-static struct attribute_group pm_attr_group = {
+static struct attribute_group pm_wakeup_attr_group = {
 	.name	= power_group_name,
-	.attrs	= power_attrs,
+	.attrs	= wakeup_attrs,
 };
 
-#ifdef CONFIG_PM_RUNTIME
-
 static struct attribute *runtime_attrs[] = {
+#ifdef CONFIG_PM_RUNTIME
 #ifndef CONFIG_PM_ADVANCED_DEBUG
 	&dev_attr_runtime_status.attr,
 #endif
···
 	&dev_attr_runtime_suspended_time.attr,
 	&dev_attr_runtime_active_time.attr,
 	&dev_attr_autosuspend_delay_ms.attr,
+#endif /* CONFIG_PM_RUNTIME */
 	NULL,
 };
 static struct attribute_group pm_runtime_attr_group = {
···
 	int rc;
 
 	rc = sysfs_create_group(&dev->kobj, &pm_attr_group);
-	if (rc == 0 && !dev->power.no_callbacks) {
+	if (rc)
+		return rc;
+
+	if (pm_runtime_callbacks_present(dev)) {
 		rc = sysfs_merge_group(&dev->kobj, &pm_runtime_attr_group);
 		if (rc)
-			sysfs_remove_group(&dev->kobj, &pm_attr_group);
+			goto err_out;
 	}
+
+	if (device_can_wakeup(dev)) {
+		rc = sysfs_merge_group(&dev->kobj, &pm_wakeup_attr_group);
+		if (rc) {
+			if (pm_runtime_callbacks_present(dev))
+				sysfs_unmerge_group(&dev->kobj,
+						    &pm_runtime_attr_group);
+			goto err_out;
+		}
+	}
+	return 0;
+
+ err_out:
+	sysfs_remove_group(&dev->kobj, &pm_attr_group);
 	return rc;
+}
+
+int wakeup_sysfs_add(struct device *dev)
+{
+	return sysfs_merge_group(&dev->kobj, &pm_wakeup_attr_group);
+}
+
+void wakeup_sysfs_remove(struct device *dev)
+{
+	sysfs_unmerge_group(&dev->kobj, &pm_wakeup_attr_group);
 }
 
 void rpm_sysfs_remove(struct device *dev)
···
 void dpm_sysfs_remove(struct device *dev)
 {
 	rpm_sysfs_remove(dev);
+	sysfs_unmerge_group(&dev->kobj, &pm_wakeup_attr_group);
 	sysfs_remove_group(&dev->kobj, &pm_attr_group);
 }
-
-#else /* CONFIG_PM_RUNTIME */
-
-int dpm_sysfs_add(struct device * dev)
-{
-	return sysfs_create_group(&dev->kobj, &pm_attr_group);
-}
-
-void dpm_sysfs_remove(struct device * dev)
-{
-	sysfs_remove_group(&dev->kobj, &pm_attr_group);
-}
-
-#endif

drivers/base/power/wakeup.c

···
 EXPORT_SYMBOL_GPL(device_wakeup_disable);
 
 /**
+ * device_set_wakeup_capable - Set/reset device wakeup capability flag.
+ * @dev: Device to handle.
+ * @capable: Whether or not @dev is capable of waking up the system from sleep.
+ *
+ * If @capable is set, set the @dev's power.can_wakeup flag and add its
+ * wakeup-related attributes to sysfs.  Otherwise, unset the @dev's
+ * power.can_wakeup flag and remove its wakeup-related attributes from sysfs.
+ *
+ * This function may sleep and it can't be called from any context where
+ * sleeping is not allowed.
+ */
+void device_set_wakeup_capable(struct device *dev, bool capable)
+{
+	if (!!dev->power.can_wakeup == !!capable)
+		return;
+
+	if (device_is_registered(dev)) {
+		if (capable) {
+			if (wakeup_sysfs_add(dev))
+				return;
+		} else {
+			wakeup_sysfs_remove(dev);
+		}
+	}
+	dev->power.can_wakeup = capable;
+}
+EXPORT_SYMBOL_GPL(device_set_wakeup_capable);
+
+/**
  * device_init_wakeup - Device wakeup initialization.
  * @dev: Device to handle.
  * @enable: Whether or not to enable @dev as a wakeup device.

include/linux/pm_runtime.h

···
 	return !dev->power.disable_depth;
 }
 
+static inline bool pm_runtime_callbacks_present(struct device *dev)
+{
+	return !dev->power.no_callbacks;
+}
+
 static inline void pm_runtime_mark_last_busy(struct device *dev)
 {
 	ACCESS_ONCE(dev->power.last_busy) = jiffies;
···
 static inline void pm_runtime_no_callbacks(struct device *dev) {}
 static inline void pm_runtime_irq_safe(struct device *dev) {}
 
+static inline bool pm_runtime_callbacks_present(struct device *dev) { return false; }
 static inline void pm_runtime_mark_last_busy(struct device *dev) {}
 static inline void __pm_runtime_use_autosuspend(struct device *dev,
 						bool use) {}

include/linux/pm_wakeup.h

···
  * Changes to device_may_wakeup take effect on the next pm state change.
  */
 
-static inline void device_set_wakeup_capable(struct device *dev, bool capable)
-{
-	dev->power.can_wakeup = capable;
-}
-
 static inline bool device_can_wakeup(struct device *dev)
 {
 	return dev->power.can_wakeup;
 }
-
-
 
 static inline bool device_may_wakeup(struct device *dev)
 {
···
 extern void wakeup_source_unregister(struct wakeup_source *ws);
 extern int device_wakeup_enable(struct device *dev);
 extern int device_wakeup_disable(struct device *dev);
+extern void device_set_wakeup_capable(struct device *dev, bool capable);
 extern int device_init_wakeup(struct device *dev, bool val);
 extern int device_set_wakeup_enable(struct device *dev, bool enable);
 extern void __pm_stay_awake(struct wakeup_source *ws);