CDNS_SPI_THLD
int threshold = cdns_spi_read(xspi, CDNS_SPI_THLD);
cdns_spi_write(xspi, CDNS_SPI_THLD, 1);
cdns_spi_write(xspi, CDNS_SPI_THLD, xspi->tx_fifo_depth >> 1);
cdns_spi_write(xspi, CDNS_SPI_THLD, 0x1);
cdns_spi_write(xspi, CDNS_SPI_THLD, 0xffff);
xspi->tx_fifo_depth = cdns_spi_read(xspi, CDNS_SPI_THLD) + 1;
cdns_spi_write(xspi, CDNS_SPI_THLD, 0x1);