usb: dwc3: gadget: simplify __dwc3_gadget_ep_queue()

Many of the comments in that function are really
outdated and don't match what the driver is
doing. Moreover, recent patches combined programming
model for all non-control endpoints, this gives us
an opportunity to get rid of our special cases in
__dwc3_gadget_ep_queue().
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -1063,18 +1063,6 @@ static int __dwc3_gadget_ep_queue(struct dwc3_ep *dep, struct dwc3_request *req)
 
 	trace_dwc3_ep_queue(req);
 
-	/*
-	 * We only add to our list of requests now and
-	 * start consuming the list once we get XferNotReady
-	 * IRQ.
-	 *
-	 * That way, we avoid doing anything that we don't need
-	 * to do now and defer it until the point we receive a
-	 * particular token from the Host side.
-	 *
-	 * This will also avoid Host cancelling URBs due to too
-	 * many NAKs.
-	 */
 	ret = usb_gadget_map_request(&dwc->gadget, &req->request,
 			dep->direction);
 	if (ret)
@@ -1082,37 +1070,8 @@ static int __dwc3_gadget_ep_queue(struct dwc3_ep *dep, struct dwc3_request *req)
 
 	list_add_tail(&req->list, &dep->pending_list);
 
-	/*
-	 * If there are no pending requests and the endpoint isn't already
-	 * busy, we will just start the request straight away.
-	 *
-	 * This will save one IRQ (XFER_NOT_READY) and possibly make it a
-	 * little bit faster.
-	 */
-	if (!usb_endpoint_xfer_isoc(dep->endpoint.desc)) {
-		ret = __dwc3_gadget_kick_transfer(dep, 0);
-		goto out;
-	}
-
-	/*
-	 * There are a few special cases:
-	 *
-	 * 1. XferNotReady with empty list of requests. We need to kick the
-	 *    transfer here in that situation, otherwise we will be NAKing
-	 *    forever. If we get XferNotReady before gadget driver has a
-	 *    chance to queue a request, we will ACK the IRQ but won't be
-	 *    able to receive the data until the next request is queued.
-	 *    The following code is handling exactly that.
-	 *
-	 */
-	if (dep->flags & DWC3_EP_PENDING_REQUEST) {
-		/*
-		 * If xfernotready is already elapsed and it is a case
-		 * of isoc transfer, then issue END TRANSFER, so that
-		 * you can receive xfernotready again and can have
-		 * notion of current microframe.
-		 */
-		if (usb_endpoint_xfer_isoc(dep->endpoint.desc)) {
+	if (usb_endpoint_xfer_isoc(dep->endpoint.desc) &&
+			dep->flags & DWC3_EP_PENDING_REQUEST) {
 		if (list_empty(&dep->started_list)) {
 			dwc3_stop_active_transfer(dwc, dep->number, true);
 			dep->flags = DWC3_EP_ENABLED;
@@ -1121,34 +1080,6 @@ static int __dwc3_gadget_ep_queue(struct dwc3_ep *dep, struct dwc3_request *req)
 	}
 
 	ret = __dwc3_gadget_kick_transfer(dep, 0);
-		if (!ret)
-			dep->flags &= ~DWC3_EP_PENDING_REQUEST;
-
-		goto out;
-	}
-
-	/*
-	 * 2. XferInProgress on Isoc EP with an active transfer. We need to
-	 *    kick the transfer here after queuing a request, otherwise the
-	 *    core may not see the modified TRB(s).
-	 */
-	if (usb_endpoint_xfer_isoc(dep->endpoint.desc) &&
-			(dep->flags & DWC3_EP_BUSY) &&
-			!(dep->flags & DWC3_EP_MISSED_ISOC)) {
-		WARN_ON_ONCE(!dep->resource_index);
-		ret = __dwc3_gadget_kick_transfer(dep, dep->resource_index);
-		goto out;
-	}
-
-	/*
-	 * 4. Stream Capable Bulk Endpoints. We need to start the transfer
-	 * right away, otherwise host will not know we have streams to be
-	 * handled.
-	 */
-	if (dep->stream_capable)
-		ret = __dwc3_gadget_kick_transfer(dep, 0);
-
-out:
 	if (ret && ret != -EBUSY)
 		dwc3_trace(trace_dwc3_gadget,
 				"%s: failed to kick transfers",