[alsa-devel] [Uclinux-dist-devel] [PATCH 2/5] ASoC codec: SSM2602: assign last substream to the master when shutting down

[Takashi Iwai]

At Sat, 13 Jun 2009 12:06:07 +0100,
Mark Brown wrote:
> 
> On Sat, Jun 13, 2009 at 07:03:12AM -0400, Mike Frysinger wrote:
> 
> > the first part conditionalized the constraints.  ignoring whitespace
> > changes, this is the diff:
> > +if (master_runtime->rate != 0)
> >     snd_pcm_hw_constraint_minmax(substream->runtime,
> >     ......
> > +if (master_runtime->sample_bits != 0)
> >     snd_pcm_hw_constraint_minmax(substream->runtime,
> >     ......
> 
> > or maybe that is what you're saying and i dont know alsa
> 
> That's not a bad change - there's a thin race condition if you
> simultaneously start up two applications where the primary substream
> could be there but not yet configured since stream startup is separate
> to the configuration of the stream.  It's hard but not impossible to
> reproduce.

An absolute race-free hw-constraint for multiple substreams is
actually difficult to implement.  The best practice would be to give
an error and refuse the change when any inconsistency occurs, IMO.


Takashi