APPLE_SPI_IF_XFER
u32 xfer = reg_read(spi, APPLE_SPI_IF_XFER) & reg_read(spi, APPLE_SPI_IE_XFER);
xfer = reg_read(spi, APPLE_SPI_IF_XFER);
reg_write(spi, APPLE_SPI_IF_XFER, ~0);
xfer_flags &= ~reg_read(spi, APPLE_SPI_IF_XFER);