[alsa-devel] [PATCH] ASoC: OMAP: Add checking to detect bufferless pcms

Mark Brown broonie at sirena.org.uk
Wed Apr 22 10:43:49 CEST 2009

On Wed, Apr 22, 2009 at 11:30:32AM +0300, Jarkko Nikula wrote:
> On Wed, Apr 22, 2009 at 4:56 AM, Joonyoung Shim <jy0922.shim at samsung.com>wrote:

> > +       /* return if this is a bufferless transfer e.g.
> > +        * codec <--> BT codec or GSM modem -- lg FIXME */
> >        if (!dma_data)
> > -               return -ENODEV;
> > +               return 0;

> I see exactly similar lines in s3c24xx-pcm.c but don't point now the use
> case where this is used and I don't have idea what is this all about.

The use case is for dummy DAIs used to represent bluetooth and similar -
they aren't going to do any DMA so don't pass anything to the platform.

> Is this something where DAI driver or another end of connection is used to
> provide clocking and the whole setup is then controlled with ALSA PCM API?
> Somehow I have the feeling that would there be a better way to achieve it
> than with dummy bufferless transfer?

The host isn't transferring any data at all in these cases.  Ideally
we'd support multiple platforms and there'd be a dummy platform driver
to go with the dummy DAI driver.

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