usb: dwc3: gadget: Issue END_TRANSFER to retry isoc transfer

After a number of unsuccessful start isoc attempts due to bus-expiry
status, issue END_TRANSFER command and retry on the next XferNotReady
event.
Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

drivers/usb/dwc3/gadget.c

@@ -1413,7 +1413,8 @@ static int __dwc3_gadget_start_isoc(struct dwc3_ep *dep)
 	int ret;
 	int i;
 
-	if (list_empty(&dep->pending_list)) {
+	if (list_empty(&dep->pending_list) &&
+	    list_empty(&dep->started_list)) {
 		dep->flags |= DWC3_EP_PENDING_REQUEST;
 		return -EAGAIN;
 	}
@@ -1436,6 +1437,27 @@ static int __dwc3_gadget_start_isoc(struct dwc3_ep *dep)
 			break;
 	}
 
+	/*
+	 * After a number of unsuccessful start attempts due to bus-expiry
+	 * status, issue END_TRANSFER command and retry on the next XferNotReady
+	 * event.
+	 */
+	if (ret == -EAGAIN) {
+		struct dwc3_gadget_ep_cmd_params params;
+		u32 cmd;
+
+		cmd = DWC3_DEPCMD_ENDTRANSFER |
+			DWC3_DEPCMD_CMDIOC |
+			DWC3_DEPCMD_PARAM(dep->resource_index);
+
+		dep->resource_index = 0;
+		memset(&params, 0, sizeof(params));
+
+		ret = dwc3_send_gadget_ep_cmd(dep, cmd, &params);
+		if (!ret)
+			dep->flags |= DWC3_EP_END_TRANSFER_PENDING;
+	}
+
 	return ret;
 }
 
@@ -2663,6 +2685,18 @@ static void dwc3_gadget_endpoint_transfer_not_ready(struct dwc3_ep *dep,
 		const struct dwc3_event_depevt *event)
 {
 	dwc3_gadget_endpoint_frame_from_event(dep, event);
+
+	/*
+	 * The XferNotReady event is generated only once before the endpoint
+	 * starts. It will be generated again when END_TRANSFER command is
+	 * issued. For some controller versions, the XferNotReady event may be
+	 * generated while the END_TRANSFER command is still in process. Ignore
+	 * it and wait for the next XferNotReady event after the command is
+	 * completed.
+	 */
+	if (dep->flags & DWC3_EP_END_TRANSFER_PENDING)
+		return;
+
 	(void) __dwc3_gadget_start_isoc(dep);
 }