I have checked Re: CYW43907 SPI Slave interface status but it seemed to be not helpful.
There was no information about SPI slave operation via SPI interface.
They were just talking about the gSPI slave operation via SDIO interface.
And grsr said "We're sorry but we are removing gSPI support on 43907 for broad market.".
Is this mean that 43907 could not support SPI slave mode any more?
The customer use SB-WBM-N07P1 module of SPIL by the way.