If asynchronous tranfers are supported, then there must also be a mechanism to cancel the pending transfer

include/nuttx/usb/usbhost.h

@@ -513,6 +513,28 @@
      ((drvr)->asynch(drvr,ep,buffer,buflen,callback,arg))
 #endif
 
+/************************************************************************************
+ * Name: DRVR_CANCEL
+ *
+ * Description:
+ *   Cancel a pending asynchronous transfer on an endpoint.
+ *
+ * Input Parameters:
+ *   drvr - The USB host driver instance obtained as a parameter from the call to
+ *      the class create() method.
+ *   ep - The IN or OUT endpoint descriptor for the device endpoint on which an
+ *      asynchronous transfer should be transferred.
+ *
+ * Returned Values:
+ *   On success, zero (OK) is returned. On a failure, a negated errno value is
+ *   returned indicating the nature of the failure.
+ *
+ ************************************************************************************/
+
+#ifdef CONFIG_USBHOST_ASYNCH
+#  define DRVR_CANCEL(drvr,ep) ((drvr)->cancel(drvr,ep))
+#endif
+
 /************************************************************************************
  * Name: DRVR_CONNECT
  *
@@ -823,6 +845,12 @@ struct usbhost_driver_s
                   usbhost_asynch_t callback, FAR void *arg);
 #endif
 
+#ifdef CONFIG_USBHOST_ASYNCH
+  /* Cancel any pending asynchronous transfer on an endpoint */
+
+  int (*cancel)(FAR struct usbhost_driver_s *drvr, usbhost_ep_t ep);
+#endif
+
 #ifdef CONFIG_USBHOST_HUB
   /* New connections may be detected by an attached hub.  This method is the
    * mechanism that is used by the hub class to introduce a new connection