Hello @oliverco
FlexSPI is primarily designed for interfacing with NOR/NAND Flash memory devices, but you can use it to interface other kind of SPI devices, but you should modify the device tree and maybe the driver for FleSPI.
Maybe it is preferible to use the SPI peripheral directly.
Also you can test if FlexSPI works with your device with spidev_test.
Best regards,
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Salas.