u-boot/drivers/spi/Kconfig

config DM_SPI
	bool "Enable Driver Model for SPI drivers"
	depends on DM
	help
	  Enable driver model for SPI. The SPI slave interface
	  (spi_setup_slave(), spi_xfer(), etc.) is then implemented by
	  the SPI uclass. Drivers provide methods to access the SPI
	  buses that they control. The uclass interface is defined in
	  include/spi.h. The existing spi_slave structure is attached
	  as 'parent data' to every slave on each bus. Slaves
	  typically use driver-private data instead of extending the
	  spi_slave structure.