diff --git a/drivers/usb/misc/usbtest.c b/drivers/usb/misc/usbtest.c
index 742be3c35947..054dedd28127 100644
--- a/drivers/usb/misc/usbtest.c
+++ b/drivers/usb/misc/usbtest.c
@@ -856,6 +856,11 @@ test_ctrl_queue (struct usbtest_dev *dev, struct usbtest_param *param)
 		struct urb		*u;
 		struct usb_ctrlrequest	req;
 		struct subcase		*reqp;
+
+		/* sign of this variable means:
+		 *  -: tested code must return this (negative) error code
+		 *  +: tested code may return this (negative too) error code
+		 */
 		int			expected = 0;
 
 		/* requests here are mostly expected to succeed on any