Index: uspace/drv/uhci/callback.c
===================================================================
--- uspace/drv/uhci/callback.c	(revision de0e6b3b72cdfc7d29d8455f440dcfb4fc2a9f1d)
+++ uspace/drv/uhci/callback.c	(revision 0535ee4e81e9834e6bc5d4934ebb9fdc34766648)
@@ -23,4 +23,5 @@
 	instance->buffer_size = size;
 	instance->dev = dev;
+	instance->arg = arg;
 	return EOK;
 }
@@ -40,6 +41,15 @@
 	if (instance->callback_in) {
 		assert(instance->callback_out == NULL);
+		uhci_print_verbose("Callback in: %p %x %d.\n",
+		  instance->callback_in, outcome, act_size);
 		instance->callback_in(
 		  instance->dev, act_size, outcome, instance->arg);
+	} else {
+		assert(instance->callback_out);
+		assert(instance->callback_in == NULL);
+		uhci_print_verbose("Callback out: %p %p %x %p .\n",
+		 instance->callback_out, instance->dev, outcome, instance->arg);
+		instance->callback_out(
+		  instance->dev, outcome, instance->arg);
 	}
 }