On Mon, May 18, 2020 at 07:09:20PM +0800, dillon.minfei@gmail.com wrote:

> 2, use stm32 spi's "In full-duplex (BIDIMODE=0 and RXONLY=0)", as tx_buf is
> null, we must add dummy data sent out before read data.
> so, add stm32f4_spi_tx_dummy() to handle this situation.

There are flags SPI_CONTROLLER_MUST_TX and SPI_CONTROLLER_MUST_RX flags
that the driver can set if it needs to, no need to open code this in the
driver.