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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>struct spi_message</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="re739.html" title="struct spi_transfer" /><link rel="next" href="re741.html" title="spi_write" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span>struct spi_message</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="re739.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="re741.html">Next</a></td></tr></table><hr /></div><div class="refentry" title="struct spi_message"><a id="API-struct-spi-message"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>struct spi_message —
one multi-segment SPI transaction
</p></div><div class="refsynopsisdiv" title="Synopsis"><h2>Synopsis</h2><pre class="programlisting">
struct spi_message {
struct list_head transfers;
struct spi_device * spi;
unsigned is_dma_mapped:1;
void (* complete) (void *context);
void * context;
unsigned actual_length;
int status;
struct list_head queue;
void * state;
}; </pre></div><div class="refsect1" title="Members"><a id="id3136295"></a><h2>Members</h2><div class="variablelist"><dl><dt><span class="term">transfers</span></dt><dd><p>
list of transfer segments in this transaction
</p></dd><dt><span class="term">spi</span></dt><dd><p>
SPI device to which the transaction is queued
</p></dd><dt><span class="term">is_dma_mapped</span></dt><dd><p>
if true, the caller provided both dma and cpu virtual
addresses for each transfer buffer
</p></dd><dt><span class="term">complete</span></dt><dd><p>
called to report transaction completions
</p></dd><dt><span class="term">context</span></dt><dd><p>
the argument to <code class="function">complete</code> when it's called
</p></dd><dt><span class="term">actual_length</span></dt><dd><p>
the total number of bytes that were transferred in all
successful segments
</p></dd><dt><span class="term">status</span></dt><dd><p>
zero for success, else negative errno
</p></dd><dt><span class="term">queue</span></dt><dd><p>
for use by whichever driver currently owns the message
</p></dd><dt><span class="term">state</span></dt><dd><p>
for use by whichever driver currently owns the message
</p></dd></dl></div></div><div class="refsect1" title="Description"><a id="id3136420"></a><h2>Description</h2><p>
A <em class="parameter"><code>spi_message</code></em> is used to execute an atomic sequence of data transfers,
each represented by a struct spi_transfer. The sequence is <span class="quote">“<span class="quote">atomic</span>”</span>
in the sense that no other spi_message may use that SPI bus until that
sequence completes. On some systems, many such sequences can execute as
as single programmed DMA transfer. On all systems, these messages are
queued, and might complete after transactions to other devices. Messages
sent to a given spi_device are alway executed in FIFO order.
</p><p>
The code that submits an spi_message (and its spi_transfers)
to the lower layers is responsible for managing its memory.
Zero-initialize every field you don't set up explicitly, to
insulate against future API updates. After you submit a message
and its transfers, ignore them until its completion callback.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="re739.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="re741.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"><span>struct spi_transfer</span> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> <span>spi_write</span></td></tr></table></div></body></html>
