usb: dwc3: ep0: handle unexpected XferNotReady events

Sometimes the host might be trying to initiate Data or
Status phase for an older Control transfer. In such
situations we must STALL that transfer and restart
the state machine rather than letting such situation
go through the wire.
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/ep0.c

@@ -733,6 +733,41 @@ static void dwc3_ep0_do_control_status(struct dwc3 *dwc,
 static void dwc3_ep0_xfernotready(struct dwc3 *dwc,
 		const struct dwc3_event_depevt *event)
 {
+	/*
+	 * This part is very tricky: If we has just handled
+	 * XferNotReady(Setup) and we're now expecting a
+	 * XferComplete but, instead, we receive another
+	 * XferNotReady(Setup), we should STALL and restart
+	 * the state machine.
+	 *
+	 * In all other cases, we just continue waiting
+	 * for the XferComplete event.
+	 *
+	 * We are a little bit unsafe here because we're
+	 * not trying to ensure that last event was, indeed,
+	 * XferNotReady(Setup).
+	 *
+	 * Still, we don't expect any condition where that
+	 * should happen and, even if it does, it would be
+	 * another error condition.
+	 */
+	if (dwc->ep0_next_event == DWC3_EP0_COMPLETE) {
+		switch (event->status) {
+		case DEPEVT_STATUS_CONTROL_SETUP:
+			dev_vdbg(dwc->dev, "Unexpected XferNotReady(Setup)\n");
+			dwc3_ep0_stall_and_restart(dwc);
+			break;
+		case DEPEVT_STATUS_CONTROL_DATA:
+			/* FALLTHROUGH */
+		case DEPEVT_STATUS_CONTROL_STATUS:
+			/* FALLTHROUGH */
+		default:
+			dev_vdbg(dwc->dev, "waiting for XferComplete\n");
+		}
+
+		return;
+	}
+
 	switch (event->status) {
 	case DEPEVT_STATUS_CONTROL_SETUP:
 		dev_vdbg(dwc->dev, "Control Setup\n");