RT2560_TX_RING_COUNT
if (sc->txq.queued >= RT2560_TX_RING_COUNT - 1) {
error = rt2560_alloc_tx_ring(sc, &sc->txq, RT2560_TX_RING_COUNT);
RT2560_TX_RING_COUNT << 8 |
(sc->txq.next_encrypt + 1) % RT2560_TX_RING_COUNT;
sc->txq.next = (sc->txq.next + 1) % RT2560_TX_RING_COUNT;
if (sc->txq.queued < RT2560_TX_RING_COUNT - 1) {