Update of /cvsroot/alsa/alsa-kernel/Documentation/DocBook
In directory sc8-pr-cvs1:/tmp/cvs-serv30871/Documentation/DocBook
Modified Files:
writing-an-alsa-driver.tmpl
Log Message:
updated the description of sg-buffer handlers again.
Index: writing-an-alsa-driver.tmpl
===================================================================
RCS file: /cvsroot/alsa/alsa-kernel/Documentation/DocBook/writing-an-alsa-driver.tmpl,v
retrieving revision 1.2
retrieving revision 1.3
diff -u -r1.2 -r1.3
--- writing-an-alsa-driver.tmpl 10 Jan 2003 10:34:25 -0000 1.2
+++ writing-an-alsa-driver.tmpl 17 Jan 2003 12:42:57 -0000 1.3
@@ -4462,13 +4462,12 @@
<para>
For creating the SG-buffer handler, call
- <function>snd_pcm_sgbuf_init()</function> in the
- <structfield>open</structfield> callback
- of a pcm substream (or in the constructor of the pcm).
+ <function>snd_pcm_lib_preallocate_sg_pages()</function> or
+ <function>snd_pcm_lib_preallocate_sg_pages_for_all()</function>
+ in the PCM constructor like other PCI pre-allocator.
You need to pass the
- <structname>pci_dev</structname> struct pointer of the chip
- and the default table size (which can be changed
- dynamically). The <type>snd_sg_buf_t</type> instance is created as
+ <structname>pci_dev</structname> struct pointer of the chip.
+ The <type>snd_sg_buf_t</type> instance is created as
substream->dma_private. You can cast
the pointer like:
@@ -4483,41 +4482,29 @@
</para>
<para>
- Then call <function>snd_pcm_sgbuf_alloc()</function> instead
- of normal <function>snd_pcm_lib_malloc_pages()</function> in
- <structfield>hw_params</structfield> callback. The SG-handler
- will allocate single pages
- and build the table on sgbuf->table. The pointer and the
- physical address of each page is stored in this table. You can
- get the physical address at a certain offset via
+ Then call <function>snd_pcm_lib_malloc_pages()</function>
+ in <structfield>hw_params</structfield> callback
+ as well as in the case of normal PCI buffer.
+ The SG-buffer handler will allocate the non-contiguous kernel
+ pages of the given size and map them onto the virtually contiguous
+ memory. The virtual pointer is addressed in runtime->dma_area.
+ The physical address (runtime->dma_addr) is set to zero,
+ because the buffer is physically non-contigous.
+ The physical address table is set up in sgbuf->table.
+ You can get the physical address at a certain offset via
<function>snd_pcm_sgbuf_get_addr()</function>.
</para>
<para>
When a SG-handler is used, you need to set
- <function>snd_pcm_sgbuf_ops_copy_playback</function> and
- <function>snd_pcm_ops_silence</function> as the
- <structfield>copy</structfield> and the
- <structfield>silence</structfield> callbacks, respectively.
- All the jobs described in the previous section will be done
- by these helper functions.
- Also, the <structfield>page</structfield> callback must be set as
- <function>snd_pcm_sgbuf_ops_page</function>.
+ <function>snd_pcm_sgbuf_ops_page</function> as
+ the <structfield>page</structfield> callback.
</para>
<para>
For releasing the data, call
- <function>snd_pcm_sgbuf_free()</function> in the
- <structfield>hw_free</structfield> callback, and call
- <function>snd_pcm_sgbuf_delete()</function> in the
- <structfield>close</structfield> callback (or in the destructor,
- if <function>snd_pcm_sgbuf_init()</function> was called in the
- constructor).
- </para>
-
- <para>
- Note that you must not do pre-allocation if a SG-handler is used.
- They conflict with each other.
+ <function>snd_pcm_lib_free_pages()</function> in the
+ <structfield>hw_free</structfield> callback as usual.
</para>
</section>
@@ -4550,13 +4537,6 @@
]]>
</programlisting>
</informalexample>
- </para>
-
- <para>
- You don't need <structfield>copy</structfield> and
- <structfield>silence</structfield> callbacks in this case,
- because the copy/set operations are available on the virtual
- address.
</para>
</section>
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