centos man page for spi_sync

SPI_SYNC(9)						  Serial Peripheral Interface (S					       SPI_SYNC(9)

NAME
       spi_sync - blocking/synchronous SPI data transfers

SYNOPSIS
       int spi_sync(struct spi_device * spi, struct spi_message * message);

ARGUMENTS
       spi
	   device with which data will be exchanged

       message
	   describes the data transfers

CONTEXT
       can sleep

DESCRIPTION
       This call may only be used from a context that may sleep. The sleep is non-interruptible, and has no timeout. Low-overhead controller
       drivers may DMA directly into and out of the message buffers.

       Note that the SPI device's chip select is active during the message, and then is normally disabled between messages. Drivers for some
       frequently-used devices may want to minimize costs of selecting a chip, by leaving it selected in anticipation that the next message will
       go to the same chip. (That may increase power usage.)

       Also, the caller is guaranteeing that the memory associated with the message will not be freed before this call returns.

       It returns zero on success, else a negative error code.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014							       SPI_SYNC(9)