tx_bd
txr->tx_bd_chain = kmalloc(sizeof(struct tx_bd *) * txr->tx_pages,
struct tx_bd *txbd;
struct tx_bd *txbd = NULL;
#define TOTAL_TX_BD_PER_PAGE (BCM_PAGE_SIZE / sizeof(struct tx_bd))
struct tx_bd **tx_bd_chain; /* tx_pages */