usb: dwc3: gadget: Delay starting transfer

If the END_TRANSFER command hasn't completed yet, then don't send the
START_TRANSFER command. The controller may not be able to start if
that's the case. Some controller revisions depend on this. See
commit 76a638f8 ("usb: dwc3: gadget: wait for End Transfer to
complete"). Let's only send START_TRANSFER command after the
END_TRANSFER command had completed.

Fixes: 3aec9915 ("usb: dwc3: gadget: remove DWC3_EP_END_TRANSFER_PENDING")
Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc3/core.h

@@ -690,6 +690,7 @@ struct dwc3_ep {
 #define DWC3_EP_TRANSFER_STARTED BIT(3)
 #define DWC3_EP_END_TRANSFER_PENDING BIT(4)
 #define DWC3_EP_PENDING_REQUEST	BIT(5)
+#define DWC3_EP_DELAY_START	BIT(6)
 
 	/* This last one is specific to EP0 */
 #define DWC3_EP0_DIR_IN		BIT(31)

drivers/usb/dwc3/gadget.c

@@ -1450,6 +1450,12 @@ static int __dwc3_gadget_ep_queue(struct dwc3_ep *dep, struct dwc3_request *req)
 	list_add_tail(&req->list, &dep->pending_list);
 	req->status = DWC3_REQUEST_STATUS_QUEUED;
 
+	/* Start the transfer only after the END_TRANSFER is completed */
+	if (dep->flags & DWC3_EP_END_TRANSFER_PENDING) {
+		dep->flags |= DWC3_EP_DELAY_START;
+		return 0;
+	}
+
 	/*
 	 * NOTICE: Isochronous endpoints should NEVER be prestarted. We must
 	 * wait for a XferNotReady event so we will know what's the current
@@ -2631,6 +2637,11 @@ static void dwc3_endpoint_interrupt(struct dwc3 *dwc,
 			dep->flags &= ~DWC3_EP_END_TRANSFER_PENDING;
 			dep->flags &= ~DWC3_EP_TRANSFER_STARTED;
 			dwc3_gadget_ep_cleanup_cancelled_requests(dep);
+			if ((dep->flags & DWC3_EP_DELAY_START) &&
+			    !usb_endpoint_xfer_isoc(dep->endpoint.desc))
+				__dwc3_gadget_kick_transfer(dep);
+
+			dep->flags &= ~DWC3_EP_DELAY_START;
 		}
 		break;
 	case DWC3_DEPEVT_STREAMEVT: