diff --git a/sys/dev/usb/usbdevs b/sys/dev/usb/usbdevs
index f8d98f07a91e..691f9702395d 100644
--- a/sys/dev/usb/usbdevs
+++ b/sys/dev/usb/usbdevs
@@ -39,6 +39,21 @@ $FreeBSD$
 
 /*
  * List of known USB vendors
+ *
+ * Please note that these IDs do not do anything. Adding an ID here and
+ * regenerating the usbdevs.h and usbdevs_data.h only makes a symbolic name
+ * available to the source code and does not change any functionality, nor
+ * does it make your device available to a specific driver.
+ * It will however make the descriptive string available if a device does not
+ * provide the string itself.
+ *
+ * After adding a vendor ID VNDR and a product ID PRDCT you will have the
+ * following extra defines:
+ * #define USB_VENDOR_VNDR		0x????
+ * #define USB_PRODUCT_VNDR_PRDCT	0x????
+ *
+ * You will have to add these defines to the respective probe routines to
+ * make the device recognised by the appropriate device driver.
  */
 
 vendor AOX		0x03e8	AOX, Inc.