DW_IC_TX_TL
regmap_write(dev->map, DW_IC_TX_TL, dev->tx_fifo_depth / 2);
regmap_write(dev->map, DW_IC_TX_TL, 0);
regmap_write(dev->map, DW_IC_TX_TL, buf_len - 1);
regmap_write(dev->map, DW_IC_TX_TL, 2 * (buf_len - 1));