From mboxrd@z Thu Jan  1 00:00:00 1970
From: Takashi Iwai <tiwai@suse.de>
Subject: Re: spin_lock_irqwhat ?
Date: Sun, 16 May 2004 17:00:32 +0200
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To: Giuliano Pochini <pochini@shiny.it>
Cc: alsa-devel@lists.sourceforge.net, clemens@ladisch.de
List-Id: alsa-devel@alsa-project.org

At Sat, 15 May 2004 23:37:47 +0200,
Giuliano Pochini wrote:
> 
> On Fri, 14 May 2004 12:37:46 +0200
> Takashi Iwai <tiwai@suse.de> wrote:
> 
> > > > prepare and trigger callbacks are already in irq-disabled.
> > > > i.e. you need only spin_lock() in them.
> > >
> > > Does it mean that ALSA acquires the lock only when it calls PCM callbacks,
> > > that is trigger(), etc., are atomic only wrt other PCM functions ?
> >
> > sorry i don't understand your question.
> >
> > the prepare and the trigger callbacks acquire several locks.
> > first, the global rw_lock for the pcm linking (snd_pcm_link_rwlock),
> > the group lock the substream belongs to, and the lock for the
> > substream itself.  and the first lock/unlock is done with *_irq().
> 
> Ok, are those locks acquired also before calling any other interface
> callback (control, midi...) ?  If so, it shouldn't be necessary protecting
> with a spin_lock() the code which touches the hw inside prepare().

no, all of these locks are specific to PCM.
you still likely need another spinlock for protecting the h/w
registers reading/writing.


Takashi


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