+
+static struct xhci_ring *xhci_triad_to_transfer_ring(struct xhci_hcd *xhci,
+ unsigned int slot_id, unsigned int ep_index,
+ unsigned int stream_id)
+{
+ struct xhci_virt_ep *ep;
+
+ ep = &xhci->devs[slot_id]->eps[ep_index];
+ /* Common case: no streams */
+ if (!(ep->ep_state & EP_HAS_STREAMS))
+ return ep->ring;
+
+ if (stream_id == 0) {
+ xhci_warn(xhci,
+ "WARN: Slot ID %u, ep index %u has streams, "
+ "but URB has no stream ID.\n",
+ slot_id, ep_index);
+ return NULL;
+ }
+
+ if (stream_id < ep->stream_info->num_streams)
+ return ep->stream_info->stream_rings[stream_id];
+
+ xhci_warn(xhci,
+ "WARN: Slot ID %u, ep index %u has "
+ "stream IDs 1 to %u allocated, "
+ "but stream ID %u is requested.\n",
+ slot_id, ep_index,
+ ep->stream_info->num_streams - 1,
+ stream_id);
+ return NULL;
+}
+
+/* Get the right ring for the given URB.
+ * If the endpoint supports streams, boundary check the URB's stream ID.
+ * If the endpoint doesn't support streams, return the singular endpoint ring.
+ */
+static struct xhci_ring *xhci_urb_to_transfer_ring(struct xhci_hcd *xhci,
+ struct urb *urb)
+{
+ return xhci_triad_to_transfer_ring(xhci, urb->dev->slot_id,
+ xhci_get_endpoint_index(&urb->ep->desc), urb->stream_id);
+}
+