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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>Constructor</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="ch02.html" title="Chapter 2. Basic Flow for PCI Drivers" /><link rel="prev" href="ch02s02.html" title="Full Code Example" /><link rel="next" href="ch02s04.html" title="Destructor" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Constructor</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch02s02.html">Prev</a> </td><th width="60%" align="center">Chapter 2. Basic Flow for PCI Drivers</th><td width="20%" align="right"> <a accesskey="n" href="ch02s04.html">Next</a></td></tr></table><hr /></div><div class="section" title="Constructor"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="basic-flow-constructor"></a>Constructor</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="ch02s03.html#basic-flow-constructor-device-index">1) Check and increment the device index.</a></span></dt><dt><span class="section"><a href="ch02s03.html#basic-flow-constructor-create-card">2) Create a card instance</a></span></dt><dt><span class="section"><a href="ch02s03.html#basic-flow-constructor-create-main">3) Create a main component</a></span></dt><dt><span class="section"><a href="ch02s03.html#basic-flow-constructor-main-component">4) Set the driver ID and name strings.</a></span></dt><dt><span class="section"><a href="ch02s03.html#basic-flow-constructor-create-other">5) Create other components, such as mixer, MIDI, etc.</a></span></dt><dt><span class="section"><a href="ch02s03.html#basic-flow-constructor-register-card">6) Register the card instance.</a></span></dt><dt><span class="section"><a href="ch02s03.html#basic-flow-constructor-set-pci">7) Set the PCI driver data and return zero.</a></span></dt></dl></div><p>
The real constructor of PCI drivers is the <code class="function">probe</code> callback.
The <code class="function">probe</code> callback and other component-constructors which are called
from the <code class="function">probe</code> callback should be defined with
the <em class="parameter"><code>__devinit</code></em> prefix. You
cannot use the <em class="parameter"><code>__init</code></em> prefix for them,
because any PCI device could be a hotplug device.
</p><p>
In the <code class="function">probe</code> callback, the following scheme is often used.
</p><div class="section" title="1) Check and increment the device index."><div class="titlepage"><div><div><h3 class="title"><a id="basic-flow-constructor-device-index"></a>1) Check and increment the device index.</h3></div></div></div><p>
</p><div class="informalexample"><pre class="programlisting">
static int dev;
....
if (dev >= SNDRV_CARDS)
return -ENODEV;
if (!enable[dev]) {
dev++;
return -ENOENT;
}
</pre></div><p>
where enable[dev] is the module option.
</p><p>
Each time the <code class="function">probe</code> callback is called, check the
availability of the device. If not available, simply increment
the device index and returns. dev will be incremented also
later (<a class="link" href="ch02s03.html#basic-flow-constructor-set-pci" title="7) Set the PCI driver data and return zero."><em class="citetitle">step
7</em></a>).
</p></div><div class="section" title="2) Create a card instance"><div class="titlepage"><div><div><h3 class="title"><a id="basic-flow-constructor-create-card"></a>2) Create a card instance</h3></div></div></div><p>
</p><div class="informalexample"><pre class="programlisting">
struct snd_card *card;
int err;
....
err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
</pre></div><p>
</p><p>
The details will be explained in the section
<a class="link" href="ch03.html#card-management-card-instance" title="Card Instance"><em class="citetitle">
Management of Cards and Components</em></a>.
</p></div><div class="section" title="3) Create a main component"><div class="titlepage"><div><div><h3 class="title"><a id="basic-flow-constructor-create-main"></a>3) Create a main component</h3></div></div></div><p>
In this part, the PCI resources are allocated.
</p><div class="informalexample"><pre class="programlisting">
struct mychip *chip;
....
err = snd_mychip_create(card, pci, &chip);
if (err < 0) {
snd_card_free(card);
return err;
}
</pre></div><p>
The details will be explained in the section <a class="link" href="ch04.html" title="Chapter 4. PCI Resource Management"><em class="citetitle">PCI Resource
Management</em></a>.
</p></div><div class="section" title="4) Set the driver ID and name strings."><div class="titlepage"><div><div><h3 class="title"><a id="basic-flow-constructor-main-component"></a>4) Set the driver ID and name strings.</h3></div></div></div><p>
</p><div class="informalexample"><pre class="programlisting">
strcpy(card->driver, "My Chip");
strcpy(card->shortname, "My Own Chip 123");
sprintf(card->longname, "%s at 0x%lx irq %i",
card->shortname, chip->ioport, chip->irq);
</pre></div><p>
The driver field holds the minimal ID string of the
chip. This is used by alsa-lib's configurator, so keep it
simple but unique.
Even the same driver can have different driver IDs to
distinguish the functionality of each chip type.
</p><p>
The shortname field is a string shown as more verbose
name. The longname field contains the information
shown in <code class="filename">/proc/asound/cards</code>.
</p></div><div class="section" title="5) Create other components, such as mixer, MIDI, etc."><div class="titlepage"><div><div><h3 class="title"><a id="basic-flow-constructor-create-other"></a>5) Create other components, such as mixer, MIDI, etc.</h3></div></div></div><p>
Here you define the basic components such as
<a class="link" href="ch05.html" title="Chapter 5. PCM Interface"><em class="citetitle">PCM</em></a>,
mixer (e.g. <a class="link" href="ch07.html" title="Chapter 7. API for AC97 Codec"><em class="citetitle">AC97</em></a>),
MIDI (e.g. <a class="link" href="ch08.html" title="Chapter 8. MIDI (MPU401-UART) Interface"><em class="citetitle">MPU-401</em></a>),
and other interfaces.
Also, if you want a <a class="link" href="ch12.html" title="Chapter 12. Proc Interface"><em class="citetitle">proc
file</em></a>, define it here, too.
</p></div><div class="section" title="6) Register the card instance."><div class="titlepage"><div><div><h3 class="title"><a id="basic-flow-constructor-register-card"></a>6) Register the card instance.</h3></div></div></div><p>
</p><div class="informalexample"><pre class="programlisting">
err = snd_card_register(card);
if (err < 0) {
snd_card_free(card);
return err;
}
</pre></div><p>
</p><p>
Will be explained in the section <a class="link" href="ch03s04.html" title="Registration and Release"><em class="citetitle">Management
of Cards and Components</em></a>, too.
</p></div><div class="section" title="7) Set the PCI driver data and return zero."><div class="titlepage"><div><div><h3 class="title"><a id="basic-flow-constructor-set-pci"></a>7) Set the PCI driver data and return zero.</h3></div></div></div><p>
</p><div class="informalexample"><pre class="programlisting">
pci_set_drvdata(pci, card);
dev++;
return 0;
</pre></div><p>
In the above, the card record is stored. This pointer is
used in the remove callback and power-management
callbacks, too.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch02s02.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch02.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch02s04.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Full Code Example </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Destructor</td></tr></table></div></body></html>
