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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>Chapter 14. Module Parameters</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="Writing an ALSA Driver" /><link rel="up" href="index.html" title="Writing an ALSA Driver" /><link rel="prev" href="ch13.html" title="Chapter 13. Power Management" /><link rel="next" href="ch15.html" title="Chapter 15. How To Put Your Driver Into ALSA Tree" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 14. Module Parameters</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch13.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ch15.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 14. Module Parameters"><div class="titlepage"><div><div><h2 class="title"><a id="module-parameters"></a>Chapter 14. Module Parameters</h2></div></div></div><p>
There are standard module options for ALSA. At least, each
module should have the <em class="parameter"><code>index</code></em>,
<em class="parameter"><code>id</code></em> and <em class="parameter"><code>enable</code></em>
options.
</p><p>
If the module supports multiple cards (usually up to
8 = <code class="constant">SNDRV_CARDS</code> cards), they should be
arrays. The default initial values are defined already as
constants for easier programming:
</p><div class="informalexample"><pre class="programlisting">
static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP;
</pre></div><p>
</p><p>
If the module supports only a single card, they could be single
variables, instead. <em class="parameter"><code>enable</code></em> option is not
always necessary in this case, but it would be better to have a
dummy option for compatibility.
</p><p>
The module parameters must be declared with the standard
<code class="function">module_param()()</code>,
<code class="function">module_param_array()()</code> and
<code class="function">MODULE_PARM_DESC()</code> macros.
</p><p>
The typical coding would be like below:
</p><div class="informalexample"><pre class="programlisting">
#define CARD_NAME "My Chip"
module_param_array(index, int, NULL, 0444);
MODULE_PARM_DESC(index, "Index value for " CARD_NAME " soundcard.");
module_param_array(id, charp, NULL, 0444);
MODULE_PARM_DESC(id, "ID string for " CARD_NAME " soundcard.");
module_param_array(enable, bool, NULL, 0444);
MODULE_PARM_DESC(enable, "Enable " CARD_NAME " soundcard.");
</pre></div><p>
</p><p>
Also, don't forget to define the module description, classes,
license and devices. Especially, the recent modprobe requires to
define the module license as GPL, etc., otherwise the system is
shown as <span class="quote">“<span class="quote">tainted</span>”</span>.
</p><div class="informalexample"><pre class="programlisting">
MODULE_DESCRIPTION("My Chip");
MODULE_LICENSE("GPL");
MODULE_SUPPORTED_DEVICE("{{Vendor,My Chip Name}}");
</pre></div><p>
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch13.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="ch15.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 13. Power Management </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 15. How To Put Your Driver Into ALSA Tree</td></tr></table></div></body></html>
