XHCI_EVENT_RING_SEGMENTS
size = roundup2(XHCI_EVENT_RING_SEGMENTS * XHCI_ERSTE_SIZE,
XHCI_ERSTE_SIZE * XHCI_EVENT_RING_SEGMENTS, BUS_DMASYNC_PREWRITE);
xhci_rt_write_4(sc, XHCI_ERSTSZ(0), XHCI_EVENT_RING_SEGMENTS);
XHCI_ERSTE_SIZE * XHCI_EVENT_RING_SEGMENTS);