diff --git a/include/linux/usb/composite.h b/include/linux/usb/composite.h
index 6014340ba980d..af3cd2aae4bcb 100644
--- a/include/linux/usb/composite.h
+++ b/include/linux/usb/composite.h
@@ -35,6 +35,14 @@
  * are ready. The control transfer will then be kept from completing till
  * all the function drivers that requested for USB_GADGET_DELAYED_STAUS
  * invoke usb_composite_setup_continue().
+ *
+ * NOTE: USB_GADGET_DELAYED_STATUS must not be used in UDC drivers: they
+ * must delay completing the status stage for 0-length control transfers
+ * regardless of the whether USB_GADGET_DELAYED_STATUS is returned from
+ * the gadget driver's setup() callback.
+ * Currently, a number of UDC drivers rely on USB_GADGET_DELAYED_STATUS,
+ * which is a bug. These drivers must be fixed and USB_GADGET_DELAYED_STATUS
+ * must be contained within the composite framework.
  */
 #define USB_GADGET_DELAYED_STATUS       0x7fff	/* Impossibly large value */
 
diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
index 75bda0783395a..6532beb587b19 100644
--- a/include/linux/usb/gadget.h
+++ b/include/linux/usb/gadget.h
@@ -711,6 +711,15 @@ static inline int usb_gadget_check_config(struct usb_gadget *gadget)
  * get_interface.  Setting a configuration (or interface) is where
  * endpoints should be activated or (config 0) shut down.
  *
+ * The gadget driver's setup() callback does not have to queue a response to
+ * ep0 within the setup() call, the driver can do it after setup() returns.
+ * The UDC driver must wait until such a response is queued before proceeding
+ * with the data/status stages of the control transfer.
+ *
+ * NOTE: Currently, a number of UDC drivers rely on USB_GADGET_DELAYED_STATUS
+ * being returned from the setup() callback, which is a bug. See the comment
+ * next to USB_GADGET_DELAYED_STATUS for details.
+ *
  * (Note that only the default control endpoint is supported.  Neither
  * hosts nor devices generally support control traffic except to ep0.)
  *