Signed-off-by: Takashi Iwai tiwai@suse.de --- Documentation/DocBook/writing-an-alsa-driver.tmpl | 28 +++++++++++++++++++---- 1 file changed, 23 insertions(+), 5 deletions(-)
diff --git a/Documentation/DocBook/writing-an-alsa-driver.tmpl b/Documentation/DocBook/writing-an-alsa-driver.tmpl index 6f639d9530b5..784793df81ed 100644 --- a/Documentation/DocBook/writing-an-alsa-driver.tmpl +++ b/Documentation/DocBook/writing-an-alsa-driver.tmpl @@ -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>