[2/4] ACPI / PM: Expose current status of ACPI power resources

Commit Message

Rafael Wysocki Jan. 22, 2013, 2:26 a.m. UTC

From: Rafael J. Wysocki <[e-mail]>

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]>
---
 Documentation/ABI/testing/sysfs-devices-resource_in_use |   12 +++++++
 drivers/acpi/power.c                                    |   26 +++++++++++++++-
 drivers/acpi/scan.c                                     |    3 +
 include/acpi/acpi_bus.h                                 |    1 
 4 files changed, 41 insertions(+), 1 deletion(-)


--
To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
the body of a message to [e-mail]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Comments

Greg KH Jan. 22, 2013, 11:49 p.m. UTC | #1

On Tue, Jan 22, 2013 at 03:26:29AM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <[e-mail]>
> 
> 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]>

But, as with patch 1/4, this is racy:

> @@ -723,6 +744,9 @@ int acpi_add_power_resource(acpi_handle
>  	if (result)
>  		goto err;
>  
> +	if (!device_create_file(&device->dev, &dev_attr_resource_in_use))
> +		device->remove = acpi_power_sysfs_remove;
> +

You are creating the file after userspace has been told that the device
is present.

As this looks like the first file this type of device has, maybe you
should just fix this up "properly" here, and not wait to do it later?

Your choice,

greg k-h
--
To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
the body of a message to [e-mail]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch

Index: linux-pm/include/acpi/acpi_bus.h
===================================================================
--- linux-pm.orig/include/acpi/acpi_bus.h
+++ linux-pm/include/acpi/acpi_bus.h
@@ -280,6 +280,7 @@  struct acpi_device {
 	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)
Index: linux-pm/drivers/acpi/scan.c
===================================================================
--- linux-pm.orig/drivers/acpi/scan.c
+++ linux-pm/drivers/acpi/scan.c
@@ -790,6 +790,9 @@  static void acpi_device_unregister(struc
 
 	acpi_power_add_remove_device(device, false);
 	acpi_device_remove_files(device);
+	if (device->remove)
+		device->remove(device);
+
 	device_unregister(&device->dev);
 	/*
 	 * Drop the reference counts of all power resources the device depends
Index: linux-pm/drivers/acpi/power.c
===================================================================
--- linux-pm.orig/drivers/acpi/power.c
+++ linux-pm/drivers/acpi/power.c
@@ -87,6 +87,12 @@  static DEFINE_MUTEX(power_resource_list_
                              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;
@@ -94,7 +100,7 @@  static struct acpi_power_resource *acpi_
 	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,
@@ -676,6 +682,21 @@  static void acpi_release_power_resource(
 	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;
@@ -723,6 +744,9 @@  int acpi_add_power_resource(acpi_handle
 	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);
 	mutex_unlock(&power_resource_list_lock);
Index: linux-pm/Documentation/ABI/testing/sysfs-devices-resource_in_use
===================================================================
--- /dev/null
+++ linux-pm/Documentation/ABI/testing/sysfs-devices-resource_in_use
@@ -0,0 +1,12 @@ 
+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.