GRETH_TXBD_NUM_MASK
if (greth->tx_next == GRETH_TXBD_NUM_MASK) {
if (greth->tx_next == GRETH_TXBD_NUM_MASK)
if (curr_tx == GRETH_TXBD_NUM_MASK)
#define NEXT_TX(N) (((N) + 1) & GRETH_TXBD_NUM_MASK)
#define SKIP_TX(N, C) (((N) + C) & GRETH_TXBD_NUM_MASK)