SPI_WRITE_THEN_READ(9)            Serial Peripheral Interface (S           SPI_WRITE_THEN_READ(9)



NAME
       spi_write_then_read - SPI synchronous write followed by read

SYNOPSIS
       int spi_write_then_read(struct spi_device * spi, const void * txbuf, unsigned n_tx,
                               void * rxbuf, unsigned n_rx);

ARGUMENTS
       spi
           device with which data will be exchanged

       txbuf
           data to be written (need not be dma-safe)

       n_tx
           size of txbuf, in bytes

       rxbuf
           buffer into which data will be read (need not be dma-safe)

       n_rx
           size of rxbuf, in bytes

CONTEXT
       can sleep

DESCRIPTION
       This performs a half duplex MicroWire style transaction with the device, sending txbuf and
       then reading rxbuf. The return value is zero for success, else a negative errno status
       code. This call may only be used from a context that may sleep.

       Parameters to this routine are always copied using a small buffer; portable code should
       never use this for more than 32 bytes. Performance-sensitive or bulk transfer code should
       instead use spi_{async,sync}() calls with dma-safe buffers.

RETURN
       zero on success, else a negative error code.

COPYRIGHT
Kernel Hackers Manual 4.8.                 January 2017                    SPI_WRITE_THEN_READ(9)