+ * Return number of free normal TRBs from enqueue to dequeue pointer on ring.
+ * Not counting an assumed link TRB at end of each TRBS_PER_SEGMENT sized segment.
+ * Only for transfer and command rings where driver is the producer, not for
+ * event rings.
+ */
+static unsigned int xhci_num_trbs_free(struct xhci_hcd *xhci, struct xhci_ring *ring)
+{
+ struct xhci_segment *enq_seg = ring->enq_seg;
+ union xhci_trb *enq = ring->enqueue;
+ union xhci_trb *last_on_seg;
+ unsigned int free = 0;
+ int i = 0;
+
+ /* Ring might be empty even if enq != deq if enq is left on a link trb */
+ if (trb_is_link(enq)) {
+ enq_seg = enq_seg->next;
+ enq = enq_seg->trbs;
+ }
+
+ /* Empty ring, common case, don't walk the segments */
+ if (enq == ring->dequeue)
+ return ring->num_segs * (TRBS_PER_SEGMENT - 1);
+
+ do {
+ if (ring->deq_seg == enq_seg && ring->dequeue >= enq)
+ return free + (ring->dequeue - enq);
+ last_on_seg = &enq_seg->trbs[TRBS_PER_SEGMENT - 1];
+ free += last_on_seg - enq;
+ enq_seg = enq_seg->next;
+ enq = enq_seg->trbs;
+ } while (i++ <= ring->num_segs);
+
+ return free;
+}
+
+/*