ACPI: dock: Don't eval _STA on every show_docked sysfs read

Some devices trigger a DEVICE_CHECK on every evalutation of _STA. This
can also be seen in commit 8b59560a3b
(ACPI: dock: avoid check _STA method).  If an undock is processed, the
dock driver sends a uevent and userspace might read the show_docked
property in sysfs. This causes an evaluation of _STA of the particular
device which causes the dock driver to immediately dock again.

In any case, evaluation of _STA (show_docked) does not necessarily mean
that we are docked, so check with the internal device structure.

http://bugzilla.kernel.org/show_bug.cgi?id=12360

Signed-off-by: Holger Macht <hmacht@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/dock.c

@@ -855,10 +855,14 @@ fdd_out:
 static ssize_t show_docked(struct device *dev,
 			   struct device_attribute *attr, char *buf)
 {
+	struct acpi_device *tmp;
+
 	struct dock_station *dock_station = *((struct dock_station **)
 		dev->platform_data);
-	return snprintf(buf, PAGE_SIZE, "%d\n", dock_present(dock_station));
 
+	if (ACPI_SUCCESS(acpi_bus_get_device(dock_station->handle, &tmp)))
+		return snprintf(buf, PAGE_SIZE, "1\n");
+	return snprintf(buf, PAGE_SIZE, "0\n");
 }
 static DEVICE_ATTR(docked, S_IRUGO, show_docked, NULL);