ACPI / scan: ACPI device object sysfs attribute for _STA evaluation

This patch adds a "status" attribute for an ACPI device. This status
attribute shows the value of the _STA object. The _STA object returns
current status of an ACPI device: enabled, disabled, functioning,
present.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
[rjw: Subject and changelog]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/scan.c

@@ -602,6 +602,20 @@ acpi_device_sun_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR(sun, 0444, acpi_device_sun_show, NULL);
 
+static ssize_t status_show(struct device *dev, struct device_attribute *attr,
+				char *buf) {
+	struct acpi_device *acpi_dev = to_acpi_device(dev);
+	acpi_status status;
+	unsigned long long sta;
+
+	status = acpi_evaluate_integer(acpi_dev->handle, "_STA", NULL, &sta);
+	if (ACPI_FAILURE(status))
+		return -ENODEV;
+
+	return sprintf(buf, "%llu\n", sta);
+}
+static DEVICE_ATTR_RO(status);
+
 static int acpi_device_setup_files(struct acpi_device *dev)
 {
 	struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER, NULL};
@@ -657,6 +671,12 @@ static int acpi_device_setup_files(struct acpi_device *dev)
 		dev->pnp.sun = (unsigned long)-1;
 	}
 
+	if (acpi_has_method(dev->handle, "_STA")) {
+		result = device_create_file(&dev->dev, &dev_attr_status);
+		if (result)
+			goto end;
+	}
+
         /*
          * If device has _EJ0, 'eject' file is created that is used to trigger
          * hot-removal function from userland.
@@ -712,6 +732,8 @@ static void acpi_device_remove_files(struct acpi_device *dev)
 		device_remove_file(&dev->dev, &dev_attr_adr);
 	device_remove_file(&dev->dev, &dev_attr_modalias);
 	device_remove_file(&dev->dev, &dev_attr_hid);
+	if (acpi_has_method(dev->handle, "_STA"))
+		device_remove_file(&dev->dev, &dev_attr_status);
 	if (dev->handle)
 		device_remove_file(&dev->dev, &dev_attr_path);
 }