ENETC_TBPIR
tx_ring->next_to_use = enetc_txbdr_rd(hw, idx, ENETC_TBPIR);
enetc_txbdr_wr(hw, idx, ENETC_TBPIR, 0);
tx_ring->tpir = hw->reg + ENETC_BDR(TX, idx, ENETC_TBPIR);
ENETC_TBPIR, ENETC_TBCIR, ENETC_TBLENR, ENETC_TBIER, ENETC_TBICR0,