SW_TXBD_RING_SIZE
rmem->vmem_size = SW_TXBD_RING_SIZE * bn->tx_nr_pages;
txr->tx_buf_ring = kzalloc(SW_TXBD_RING_SIZE, GFP_KERNEL);
rmem->vmem_size = SW_TXBD_RING_SIZE * bp->tx_nr_pages;