'\" t
.\"     Title: spi_write_then_read
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\"      Date: January 2017
.\"    Manual: Serial Peripheral Interface (SPI)
.\"    Source: Kernel Hackers Manual 4.8.15
.\"  Language: English
.\"
.TH "SPI_WRITE_THEN_READ" "9" "January 2017" "Kernel Hackers Manual 4\&.8\&." "Serial Peripheral Interface (S"
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.SH "NAME"
spi_write_then_read \- SPI synchronous write followed by read
.SH "SYNOPSIS"
.HP \w'int\ spi_write_then_read('u
.BI "int spi_write_then_read(struct\ spi_device\ *\ " "spi" ", const\ void\ *\ " "txbuf" ", unsigned\ " "n_tx" ", void\ *\ " "rxbuf" ", unsigned\ " "n_rx" ");"
.SH "ARGUMENTS"
.PP
\fIspi\fR
.RS 4
device with which data will be exchanged
.RE
.PP
\fItxbuf\fR
.RS 4
data to be written (need not be dma\-safe)
.RE
.PP
\fIn_tx\fR
.RS 4
size of txbuf, in bytes
.RE
.PP
\fIrxbuf\fR
.RS 4
buffer into which data will be read (need not be dma\-safe)
.RE
.PP
\fIn_rx\fR
.RS 4
size of rxbuf, in bytes
.RE
.SH "CONTEXT"
.PP
can sleep
.SH "DESCRIPTION"
.PP
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\&.
.PP
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\&.
.SH "RETURN"
.PP
zero on success, else a negative error code\&.
.SH "COPYRIGHT"
.br