RT2560_TX_RING_COUNT
sc->txq.next = (sc->txq.next + 1) % RT2560_TX_RING_COUNT;
sc->txq.queued < (RT2560_TX_RING_COUNT - 32)) {
if (sc->txq.queued >= RT2560_TX_RING_COUNT - 1) {
sc->txq.cur = (sc->txq.cur + 1) % RT2560_TX_RING_COUNT;
err = rt2560_alloc_tx_ring(sc, &sc->txq, RT2560_TX_RING_COUNT);
RT2560_TX_RING_COUNT << 8 |