+/*
+ * Returns the number of packets in the last "burst" of packets. This field is
+ * valid for all speeds of devices. USB 2.0 devices can only do one "burst", so
+ * the last burst packet count is equal to the total number of packets in the
+ * TD. SuperSpeed endpoints can have up to 3 bursts. All but the last burst
+ * must contain (bMaxBurst + 1) number of packets, but the last burst can
+ * contain 1 to (bMaxBurst + 1) packets.
+ */
+static unsigned int xhci_get_last_burst_packet_count(struct xhci_hcd *xhci,
+ struct usb_device *udev,
+ struct urb *urb, unsigned int total_packet_count)
+{
+ unsigned int max_burst;
+ unsigned int residue;
+
+ if (xhci->hci_version < 0x100)
+ return 0;
+
+ switch (udev->speed) {
+ case USB_SPEED_SUPER:
+ /* bMaxBurst is zero based: 0 means 1 packet per burst */
+ max_burst = urb->ep->ss_ep_comp.bMaxBurst;
+ residue = total_packet_count % (max_burst + 1);
+ /* If residue is zero, the last burst contains (max_burst + 1)
+ * number of packets, but the TLBPC field is zero-based.
+ */
+ if (residue == 0)
+ return max_burst;
+ return residue - 1;
+ default:
+ if (total_packet_count == 0)
+ return 0;
+ return total_packet_count - 1;
+ }
+}
+