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ALSA: Update document about PCM nonatomic ops

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Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2014-09-15 15:22:02 +02:00
parent 3b73cfe559
commit 941a74ca9e
1 changed files with 23 additions and 5 deletions
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28
Documentation/DocBook/writing-an-alsa-driver.tmpl
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@ -2742,7 +2742,9 @@ struct _snd_pcm_runtime {
<para>
Another note is that this callback is non-atomic
(schedulable). This is important, because the
(schedulable) as default, i.e. when no
<structfield>nonatomic</structfield> flag set.
This is important, because the
<structfield>trigger</structfield> callback
is atomic (non-schedulable). That is, mutexes or any
schedule-related functions are not available in
@ -2900,8 +2902,9 @@ struct _snd_pcm_runtime {
</para>
<para>
As mentioned, this callback is atomic. You cannot call
functions which may sleep.
As mentioned, this callback is atomic as default unless
<structfield>nonatomic</structfield> flag set, and
you cannot call functions which may sleep.
The trigger callback should be as minimal as possible,
just really triggering the DMA. The other stuff should be
initialized hw_params and prepare callbacks properly
@ -2936,7 +2939,7 @@ struct _snd_pcm_runtime {
</para>
<para>
This callback is also atomic.
This callback is also atomic as default.
</para>
</section>
@ -2972,7 +2975,7 @@ struct _snd_pcm_runtime {
is useful only for such a purpose.
</para>
<para>
This callback is atomic.
This callback is atomic as default.
</para>
</section>
@ -3175,6 +3178,21 @@ struct _snd_pcm_runtime {
called with local interrupts disabled.
</para>
<para>
The recent changes in PCM core code, however, allow all PCM
operations to be non-atomic. This assumes that the all caller
sides are in non-atomic contexts. For example, the function
<function>snd_pcm_period_elapsed()</function> is called
typically from the interrupt handler. But, if you set up the
driver to use a threaded interrupt handler, this call can be in
non-atomic context, too. In such a case, you can set
<structfield>nonatomic</structfield> filed of
<structname>snd_pcm</structname> object after creating it.
When this flag is set, mutex and rwsem are used internally in
the PCM core instead of spin and rwlocks, so that you can call
all PCM functions safely in a non-atomic context.
</para>
</section>
<section id="pcm-interface-constraints">
<title>Constraints</title>