ACPI / PM: Expose current status of ACPI power resources

Since ACPI power resources are going to be used more extensively on
new hardware platforms, it becomes necessary for user space (powertop
in particular) to observe some properties of those resources for
diagnostics purposes.

For this reason, expose the current status of each ACPI power
resource to user space via sysfs by adding a new resource_in_use
attribute to the sysfs directory representing the given power
resource.

Signed-off-by: Rafael J. Wysocki <[e-mail]>
Acked-by: Greg Kroah-Hartman <[e-mail]>

Documentation/ABI/testing/sysfs-devices-resource_in_use

···
+What:		/sys/devices/.../resource_in_use
+Date:		January 2013
+Contact:	Rafael J. Wysocki <[e-mail]>
+Description:
+		The /sys/devices/.../resource_in_use attribute is only present
+		for device objects representing ACPI power resources.
+
+		If present, it contains a number (0 or 1) representing the
+		current status of the given power resource (0 means that the
+		resource is not in use and therefore it has been turned off).
+
+		This attribute is read-only.

drivers/acpi/power.c

···
                              Power Resource Management
    -------------------------------------------------------------------------- */
 
+static inline
+struct acpi_power_resource *to_power_resource(struct acpi_device *device)
+{
+	return container_of(device, struct acpi_power_resource, device);
+}
+
 static struct acpi_power_resource *acpi_power_get_context(acpi_handle handle)
 {
 	struct acpi_device *device;
···
 	if (acpi_bus_get_device(handle, &device))
 		return NULL;
 
-	return container_of(device, struct acpi_power_resource, device);
+	return to_power_resource(device);
 }
 
 static int acpi_power_resources_list_add(acpi_handle handle,
···
 	kfree(resource);
 }
 
+static ssize_t acpi_power_in_use_show(struct device *dev,
+				      struct device_attribute *attr,
+				      char *buf) {
+	struct acpi_power_resource *resource;
+
+	resource = to_power_resource(to_acpi_device(dev));
+	return sprintf(buf, "%u\n", !!resource->ref_count);
+}
+static DEVICE_ATTR(resource_in_use, 0444, acpi_power_in_use_show, NULL);
+
+static void acpi_power_sysfs_remove(struct acpi_device *device)
+{
+	device_remove_file(&device->dev, &dev_attr_resource_in_use);
+}
+
 int acpi_add_power_resource(acpi_handle handle)
 {
 	struct acpi_power_resource *resource;
···
 	result = acpi_device_add(device, acpi_release_power_resource);
 	if (result)
 		goto err;
+
+	if (!device_create_file(&device->dev, &dev_attr_resource_in_use))
+		device->remove = acpi_power_sysfs_remove;
 
 	mutex_lock(&power_resource_list_lock);
 	list_add(&resource->list_node, &acpi_power_resource_list);

drivers/acpi/scan.c

···
 
 	acpi_power_add_remove_device(device, false);
 	acpi_device_remove_files(device);
+	if (device->remove)
+		device->remove(device);
+
 	device_del(&device->dev);
 	/*
 	 * Drop the reference counts of all power resources the device depends

include/acpi/acpi_bus.h

···
 	struct mutex physical_node_lock;
 	DECLARE_BITMAP(physical_node_id_bitmap, ACPI_MAX_PHYSICAL_NODE);
 	struct list_head power_dependent;
+	void (*remove)(struct acpi_device *);
 };
 
 static inline void *acpi_driver_data(struct acpi_device *d)