usb: dwc3: gadget: Check for number of TRBs prepared

By returning the number of TRBs prepared, we know whether to execute
__dwc3_gadget_kick_transfer(). This allows us to check if we ran out of
TRBs when extra TRBs are needed for OUT transfers. It also allows us to
properly handle usb_gadget_map_request_by_dev() error.

Fixes: c6267a51 ("usb: dwc3: gadget: align transfers to wMaxPacketSize")
Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

drivers/usb/dwc3/gadget.c

@@ -1257,10 +1257,13 @@ static int dwc3_prepare_one_trb_linear(struct dwc3_ep *dep,
  * The function goes through the requests list and sets up TRBs for the
  * transfers. The function returns once there are no more TRBs available or
  * it runs out of requests.
+ *
+ * Returns the number of TRBs prepared or negative errno.
  */
-static void dwc3_prepare_trbs(struct dwc3_ep *dep)
+static int dwc3_prepare_trbs(struct dwc3_ep *dep)
 {
 	struct dwc3_request	*req, *n;
+	int			ret = 0;
 
 	BUILD_BUG_ON_NOT_POWER_OF_2(DWC3_TRB_NUM);
 
@@ -1275,11 +1278,14 @@ static void dwc3_prepare_trbs(struct dwc3_ep *dep)
 	 * break things.
 	 */
 	list_for_each_entry(req, &dep->started_list, list) {
-		if (req->num_pending_sgs > 0)
-			dwc3_prepare_one_trb_sg(dep, req);
+		if (req->num_pending_sgs > 0) {
+			ret = dwc3_prepare_one_trb_sg(dep, req);
+			if (!ret)
+				return ret;
+		}
 
 		if (!dwc3_calc_trbs_left(dep))
-			return;
+			return ret;
 
 		/*
 		 * Don't prepare beyond a transfer. In DWC_usb32, its transfer
@@ -1287,17 +1293,16 @@ static void dwc3_prepare_trbs(struct dwc3_ep *dep)
 		 * active transfer instead of stopping.
 		 */
 		if (dep->stream_capable && req->request.is_last)
-			return;
+			return ret;
 	}
 
 	list_for_each_entry_safe(req, n, &dep->pending_list, list) {
 		struct dwc3	*dwc = dep->dwc;
-		int		ret;
 
 		ret = usb_gadget_map_request_by_dev(dwc->sysdev, &req->request,
 						    dep->direction);
 		if (ret)
-			return;
+			return ret;
 
 		req->sg			= req->request.sg;
 		req->start_sg		= req->sg;
@@ -1305,12 +1310,12 @@ static void dwc3_prepare_trbs(struct dwc3_ep *dep)
 		req->num_pending_sgs	= req->request.num_mapped_sgs;
 
 		if (req->num_pending_sgs > 0)
-			dwc3_prepare_one_trb_sg(dep, req);
+			ret = dwc3_prepare_one_trb_sg(dep, req);
 		else
-			dwc3_prepare_one_trb_linear(dep, req);
+			ret = dwc3_prepare_one_trb_linear(dep, req);
 
-		if (!dwc3_calc_trbs_left(dep))
-			return;
+		if (!ret || !dwc3_calc_trbs_left(dep))
+			return ret;
 
 		/*
 		 * Don't prepare beyond a transfer. In DWC_usb32, its transfer
@@ -1318,8 +1323,10 @@ static void dwc3_prepare_trbs(struct dwc3_ep *dep)
 		 * active transfer instead of stopping.
 		 */
 		if (dep->stream_capable && req->request.is_last)
-			return;
+			return ret;
 	}
+
+	return ret;
 }
 
 static void dwc3_gadget_ep_cleanup_cancelled_requests(struct dwc3_ep *dep);
@@ -1332,12 +1339,12 @@ static int __dwc3_gadget_kick_transfer(struct dwc3_ep *dep)
 	int				ret;
 	u32				cmd;
 
-	if (!dwc3_calc_trbs_left(dep))
-		return 0;
+	ret = dwc3_prepare_trbs(dep);
+	if (ret <= 0)
+		return ret;
 
 	starting = !(dep->flags & DWC3_EP_TRANSFER_STARTED);
 
-	dwc3_prepare_trbs(dep);
 	req = next_request(&dep->started_list);
 	if (!req) {
 		dep->flags |= DWC3_EP_PENDING_REQUEST;