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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>Vmalloc'ed Buffers</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="ch11.html" title="Chapter 11. Buffer and Memory Management" /><link rel="prev" href="ch11s03.html" title="Non-Contiguous Buffers" /><link rel="next" href="ch12.html" title="Chapter 12. Proc Interface" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Vmalloc'ed Buffers</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch11s03.html">Prev</a> </td><th width="60%" align="center">Chapter 11. Buffer and Memory Management</th><td width="20%" align="right"> <a accesskey="n" href="ch12.html">Next</a></td></tr></table><hr /></div><div class="section" title="Vmalloc'ed Buffers"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="buffer-and-memory-vmalloced"></a>Vmalloc'ed Buffers</h2></div></div></div><p>
It's possible to use a buffer allocated via
<code class="function">vmalloc</code>, for example, for an intermediate
buffer. Since the allocated pages are not contiguous, you need
to set the <em class="structfield"><code>page</code></em> callback to obtain
the physical address at every offset.
</p><p>
The implementation of <em class="structfield"><code>page</code></em> callback
would be like this:
</p><div class="informalexample"><pre class="programlisting">
#include <linux/vmalloc.h>
/* get the physical page pointer on the given offset */
static struct page *mychip_page(struct snd_pcm_substream *substream,
unsigned long offset)
{
void *pageptr = substream->runtime->dma_area + offset;
return vmalloc_to_page(pageptr);
}
</pre></div><p>
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