ACPI / PM: Expose power states of ACPI devices to user space

Make it possible to retrieve the current power state of a device with
ACPI power management from user space via sysfs by adding two new
attributes, power_state and real_power_state, to the sysfs directory
associated with the struct acpi_device object representing the
device's ACPI node.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 91 insertions, 1 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-power_state b/Documentation/ABI/testing/sysfs-devices-power_state
new file mode 100644
index 000000000000..7ad9546748f0
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-power_state
@@ -0,0 +1,20 @@
+What:           /sys/devices/.../power_state
+Date:           January 2013
+Contact:        Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+Description:
+                The /sys/devices/.../power_state attribute is only present for
+                device objects representing ACPI device nodes that provide power
+                management methods.
+
+                If present, it contains a string representing the current ACPI
+                power state of the given device node.  Its possible values,
+                "D0", "D1", "D2", "D3hot", and "D3cold", reflect the power state
+                names defined by the ACPI specification (ACPI 4 and above).
+
+                If the device node uses shared ACPI power resources, this state
+                determines a list of power resources required not to be turned
+                off.  However, some power resources needed by the device node in
+                higher-power (lower-number) states may also be ON because of
+                some other devices using them at the moment.
+
+                This attribute is read-only.
diff --git a/Documentation/ABI/testing/sysfs-devices-real_power_state b/Documentation/ABI/testing/sysfs-devices-real_power_state
new file mode 100644
index 000000000000..8b3527c82a7d
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-real_power_state
@@ -0,0 +1,23 @@
+What:           /sys/devices/.../real_power_state
+Date:           January 2013
+Contact:        Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+Description:
+                The /sys/devices/.../real_power_state attribute is only present
+                for device objects representing ACPI device nodes that provide
+                power management methods and use ACPI power resources for power
+                management.
+
+                If present, it contains a string representing the real ACPI
+                power state of the given device node as returned by the _PSC
+                control method or inferred from the configuration of power
+                resources.  Its possible values, "D0", "D1", "D2", "D3hot", and
+                "D3cold", reflect the power state names defined by the ACPI
+                specification (ACPI 4 and above).
+
+                In some situations the value of this attribute may be different
+                from the value of the /sys/devices/.../power_state attribute for
+                the same device object.  If that happens, some shared power
+                resources used by the device node are only ON because of some
+                other devices using them at the moment.
+
+                This attribute is read-only.
diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 8b3b18846c8c..9761d589f3f5 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -178,6 +178,32 @@ err_out:
 }
 EXPORT_SYMBOL(acpi_bus_hot_remove_device);
 
+static ssize_t real_power_state_show(struct device *dev,
+                                     struct device_attribute *attr, char *buf)
+{
+        struct acpi_device *adev = to_acpi_device(dev);
+        int state;
+        int ret;
+
+        ret = acpi_device_get_power(adev, &state);
+        if (ret)
+                return ret;
+
+        return sprintf(buf, "%s\n", acpi_power_state_string(state));
+}
+
+static DEVICE_ATTR(real_power_state, 0444, real_power_state_show, NULL);
+
+static ssize_t power_state_show(struct device *dev,
+                                struct device_attribute *attr, char *buf)
+{
+        struct acpi_device *adev = to_acpi_device(dev);
+
+        return sprintf(buf, "%s\n", acpi_power_state_string(adev->power.state));
+}
+
+static DEVICE_ATTR(power_state, 0444, power_state_show, NULL);
+
 static ssize_t
 acpi_eject_store(struct device *d, struct device_attribute *attr,
                 const char *buf, size_t count)
@@ -369,8 +395,22 @@ static int acpi_device_setup_files(struct acpi_device *dev)
          * hot-removal function from userland.
          */
         status = acpi_get_handle(dev->handle, "_EJ0", &temp);
-        if (ACPI_SUCCESS(status))
+        if (ACPI_SUCCESS(status)) {
                 result = device_create_file(&dev->dev, &dev_attr_eject);
+                if (result)
+                        return result;
+        }
+
+        if (dev->flags.power_manageable) {
+                result = device_create_file(&dev->dev, &dev_attr_power_state);
+                if (result)
+                        return result;
+
+                if (dev->power.flags.power_resources)
+                        result = device_create_file(&dev->dev,
+                                                    &dev_attr_real_power_state);
+        }
+
 end:
         return result;
 }
@@ -380,6 +420,13 @@ static void acpi_device_remove_files(struct acpi_device *dev)
         acpi_status status;
         acpi_handle temp;
 
+        if (dev->flags.power_manageable) {
+                device_remove_file(&dev->dev, &dev_attr_power_state);
+                if (dev->power.flags.power_resources)
+                        device_remove_file(&dev->dev,
+                                           &dev_attr_real_power_state);
+        }
+
         /*
          * If device has _STR, remove 'description' file
          */