usb: dwc3: gadget: only unmap requests from DMA if mapped

A recent optimization was made so that a request put on the
pending_list wouldn't get mapped for DMA until just before
preparing a TRB for it. However, this poses a problem in case
the request is dequeued or the endpoint is disabled before the
mapping is done as that would lead to dwc3_gadget_giveback()
unconditionally calling usb_gadget_unmap_request_for_dev() with
an invalid request->dma handle. Depending on the platform's DMA
implementation the unmap operation could result in a panic.

Since we know a successful mapping is a prerequisite for getting
a TRB, the unmap can be conditionally called only when req->trb
is non-NULL.

Fixes: cdb55b39fab8 ("usb: dwc3: gadget: lazily map requests for DMA")
Signed-off-by: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -191,14 +191,16 @@ void dwc3_gadget_giveback(struct dwc3_ep *dep, struct dwc3_request *req,
 
 	req->started = false;
 	list_del(&req->list);
-	req->trb = NULL;
 	req->remaining = 0;
 
 	if (req->request.status == -EINPROGRESS)
 		req->request.status = status;
 
-	usb_gadget_unmap_request_by_dev(dwc->sysdev,
-					&req->request, req->direction);
+	if (req->trb)
+		usb_gadget_unmap_request_by_dev(dwc->sysdev,
+						&req->request, req->direction);
+
+	req->trb = NULL;
 
 	trace_dwc3_gadget_giveback(req);