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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>spi_write_then_read</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="Linux Device Drivers" /><link rel="up" href="ch09.html" title="Chapter 9. Serial Peripheral Interface (SPI)" /><link rel="prev" href="re752.html" title="spi_sync" /><link rel="next" href="ch10.html" title="Chapter 10. I2C and SMBus Subsystem" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span>spi_write_then_read</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="re752.html">Prev</a> </td><th width="60%" align="center">Chapter 9. Serial Peripheral Interface (SPI)</th><td width="20%" align="right"> <a accesskey="n" href="ch10.html">Next</a></td></tr></table><hr /></div><div class="refentry" title="spi_write_then_read"><a id="API-spi-write-then-read"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>spi_write_then_read —
SPI synchronous write followed by read
</p></div><div class="refsynopsisdiv" title="Synopsis"><h2>Synopsis</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">spi_write_then_read </b>(</code></td><td>struct spi_device * <var class="pdparam">spi</var>, </td></tr><tr><td> </td><td>const u8 * <var class="pdparam">txbuf</var>, </td></tr><tr><td> </td><td>unsigned <var class="pdparam">n_tx</var>, </td></tr><tr><td> </td><td>u8 * <var class="pdparam">rxbuf</var>, </td></tr><tr><td> </td><td>unsigned <var class="pdparam">n_rx</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" title="Arguments"><a id="id2708018"></a><h2>Arguments</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>spi</code></em></span></dt><dd><p>
device with which data will be exchanged
</p></dd><dt><span class="term"><em class="parameter"><code>txbuf</code></em></span></dt><dd><p>
data to be written (need not be dma-safe)
</p></dd><dt><span class="term"><em class="parameter"><code>n_tx</code></em></span></dt><dd><p>
size of txbuf, in bytes
</p></dd><dt><span class="term"><em class="parameter"><code>rxbuf</code></em></span></dt><dd><p>
buffer into which data will be read (need not be dma-safe)
</p></dd><dt><span class="term"><em class="parameter"><code>n_rx</code></em></span></dt><dd><p>
size of rxbuf, in bytes
</p></dd></dl></div></div><div class="refsect1" title="Context"><a id="id2708114"></a><h2>Context</h2><p>
can sleep
</p></div><div class="refsect1" title="Description"><a id="id2708125"></a><h2>Description</h2><p>
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.
</p><p>
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.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="re752.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch09.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch10.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"><span>spi_sync</span> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 10. I<sup>2</sup>C and SMBus Subsystem</td></tr></table></div></body></html>
