spi_write_then_read — SPI synchronous write followed by read
int spi_write_then_read ( | struct spi_device * | spi, |
| const u8 * | txbuf, | |
| unsigned | n_tx, | |
| u8 * | rxbuf, | |
| unsigned | n_rx); |
spidevice with which data will be exchanged
txbufdata to be written (need not be dma-safe)
n_txsize of txbuf, in bytes
rxbufbuffer into which data will be read
n_rxsize of rxbuf, in bytes (need not be dma-safe)
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.