On Mon,  3 Sep 2018 19:13:16 +0300
Arseny Maslennikov [off-list ref] wrote:

+	if (ndev->dev_id == ndev->dev_port) {
+		netdev_info_once(ndev,
+			"\"%s\" wants to know my dev_id. "
+			"Should it look at dev_port instead?\n",
+			current->comm);
+		netdev_info_once(ndev,
+			"See Documentation/ABI/testing/sysfs-class-net for more info.\n");
+	}

Single line message is sufficient.
Also don't break strings in messages.

+	}
+
+	ret = sprintf(buf, "%#x\n", ndev->dev_id);
+
+	return ret;

Why not?
	return sprintf...