HID: cougar: make compare_device_paths reusable

The function compare_device_paths from wacom_sys.c is generic
and useful for other drivers. Move the function to hid-core and
rename it as hid_compare_device_paths.
Signed-off-by: Daniel M. Lambea <dmlambea@gmail.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-core.c

@@ -1939,6 +1939,29 @@ static int hid_bus_match(struct device *dev, struct device_driver *drv)
 	return hid_match_device(hdev, hdrv) != NULL;
 }
 
+/**
+ * hid_compare_device_paths - check if both devices share the same path
+ * @hdev_a: hid device
+ * @hdev_b: hid device
+ * @separator: char to use as separator
+ *
+ * Check if two devices share the same path up to the last occurrence of
+ * the separator char. Both paths must exist (i.e., zero-length paths
+ * don't match).
+ */
+bool hid_compare_device_paths(struct hid_device *hdev_a,
+			      struct hid_device *hdev_b, char separator)
+{
+	int n1 = strrchr(hdev_a->phys, separator) - hdev_a->phys;
+	int n2 = strrchr(hdev_b->phys, separator) - hdev_b->phys;
+
+	if (n1 != n2 || n1 <= 0 || n2 <= 0)
+		return false;
+
+	return !strncmp(hdev_a->phys, hdev_b->phys, n1);
+}
+EXPORT_SYMBOL_GPL(hid_compare_device_paths);
+
 static int hid_device_probe(struct device *dev)
 {
 	struct hid_driver *hdrv = to_hid_driver(dev->driver);

drivers/hid/wacom_sys.c

@@ -703,18 +703,6 @@ struct wacom_hdev_data {
 static LIST_HEAD(wacom_udev_list);
 static DEFINE_MUTEX(wacom_udev_list_lock);
 
-static bool compare_device_paths(struct hid_device *hdev_a,
-		struct hid_device *hdev_b, char separator)
-{
-	int n1 = strrchr(hdev_a->phys, separator) - hdev_a->phys;
-	int n2 = strrchr(hdev_b->phys, separator) - hdev_b->phys;
-
-	if (n1 != n2 || n1 <= 0 || n2 <= 0)
-		return false;
-
-	return !strncmp(hdev_a->phys, hdev_b->phys, n1);
-}
-
 static bool wacom_are_sibling(struct hid_device *hdev,
 		struct hid_device *sibling)
 {
@@ -737,10 +725,10 @@ static bool wacom_are_sibling(struct hid_device *hdev,
 	 * the same physical parent device path.
 	 */
 	if (hdev->vendor == sibling->vendor && hdev->product == sibling->product) {
-		if (!compare_device_paths(hdev, sibling, '/'))
+		if (!hid_compare_device_paths(hdev, sibling, '/'))
 			return false;
 	} else {
-		if (!compare_device_paths(hdev, sibling, '.'))
+		if (!hid_compare_device_paths(hdev, sibling, '.'))
 			return false;
 	}
 
@@ -787,7 +775,7 @@ static struct wacom_hdev_data *wacom_get_hdev_data(struct hid_device *hdev)
 
 	/* Try to find an already-probed interface from the same device */
 	list_for_each_entry(data, &wacom_udev_list, list) {
-		if (compare_device_paths(hdev, data->dev, '/')) {
+		if (hid_compare_device_paths(hdev, data->dev, '/')) {
 			kref_get(&data->kref);
 			return data;
 		}

include/linux/hid.h

@@ -894,6 +894,8 @@ const struct hid_device_id *hid_match_id(const struct hid_device *hdev,
 					 const struct hid_device_id *id);
 const struct hid_device_id *hid_match_device(struct hid_device *hdev,
 					     struct hid_driver *hdrv);
+bool hid_compare_device_paths(struct hid_device *hdev_a,
+			      struct hid_device *hdev_b, char separator);
 s32 hid_snto32(__u32 value, unsigned n);
 __u32 hid_field_extract(const struct hid_device *hid, __u8 *report,
 		     unsigned offset, unsigned n);