usb: dwc3: gadget: Set IOC if not enough for extra TRBs

If we run out of TRBs because we need extra TRBs, make sure to set the
IOC bit for the previously prepared TRB to get completion notification
to free up TRBs to resume later.
Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

drivers/usb/dwc3/gadget.c

@@ -1197,7 +1197,27 @@ static int dwc3_prepare_one_trb_sg(struct dwc3_ep *dep,
 			break;
 	}
 
+	return req->num_trbs - num_trbs;
+
 out:
+	/*
+	 * If we run out of TRBs for MPS alignment setup, then set IOC on the
+	 * previous TRB to get notified for TRB completion to resume when more
+	 * TRBs are available.
+	 *
+	 * Note: normally we shouldn't update the TRB after the HWO bit is set.
+	 * However, the controller doesn't update its internal cache to handle
+	 * the newly prepared TRBs until UPDATE_TRANSFER or START_TRANSFER
+	 * command is executed. At this point, it doesn't happen yet, so we
+	 * should be fine modifying it here.
+	 */
+	if (i) {
+		struct dwc3_trb	*trb;
+
+		trb = dwc3_ep_prev_trb(dep, dep->trb_enqueue);
+		trb->ctrl |= DWC3_TRB_CTRL_IOC;
+	}
+
 	return req->num_trbs - num_trbs;
 }