Can SPI Slave mode work without Chip Select on bf609?

I have been trying to configure slave SPI on our custom board,
I see clock and MOSI working as expected (comming from another board)
but it seems it never reads it after submitting buffer (working in DMA mode) - since I never get callback and data is empty.
I am not using CS and I didn't find any information on weather it is required or can be omitted?

Best Regards