Index: uspace/drv/bus/usb/xhci/commands.c
===================================================================
--- uspace/drv/bus/usb/xhci/commands.c	(revision f711f06116f62c4ea5fb02b9075000c5692c6219)
+++ uspace/drv/bus/usb/xhci/commands.c	(revision c362127ff86c6ba802ca5edd6ed8582d9fd08ff9)
@@ -92,12 +92,22 @@
 
 	int code = XHCI_DWORD_EXTRACT(trb->status, 31, 24);
-	if (code != XHCI_TRBC_SUCCESS)
-		return EINVAL; // TODO: Find a better error code/handler.
 
 	xhci_trb_t *command = (xhci_trb_t *) XHCI_QWORD_EXTRACT(trb->parameter, 63, 4);
+
 	switch(TRB_TYPE(*command)) {
-		default:
-			// TODO:
-			break;
+	case XHCI_TRB_TYPE_NO_OP_CMD:
+		assert(code == XHCI_TRBC_TRB_ERROR);
+		break;
+	case XHCI_TRB_TYPE_ENABLE_SLOT_CMD:
+	{
+		uint32_t slot_id = XHCI_DWORD_EXTRACT(trb->control, 31, 24);
+		(void) slot_id;
+		// TODO: Call a device addition callback once it's implemented.
+		//       Also check for a suitable type of the slot id.
+		break;
+	}
+	default:
+		usb_log_warning("HC(%p) Command of an unsupported type has been completed.", hc);
+		break;
 	}