[alsa-devel] [PATCH v5 1/7] sound: codec: wm8731: add rates constraints

Mark Brown broonie at kernel.org
Mon Jul 15 17:22:28 CEST 2013

On Mon, Jul 15, 2013 at 04:53:46PM +0200, Richard Genoud wrote:
> 2013/7/12 Mark Brown <broonie at kernel.org>:

> > This isn't going to work with systems which have a variable clock as the
> > input to the CODEC.  If it's imposing constraints the driver needs to
> > allow setting the clock to zero as a way of removing constraints (and
> > any existing drivers should be updated to do this if needed).

> Maybe I'm wrong, but I didn't find any system using variable clock
> with this codec.

The driver should be written with that possibility in mind even if there
were no users; it only takes a couple of lines of code.

> The sam9g20ek (soc/atmel/sam9g20_wm8731.c) is not using a crystal, but
> it's using a fixed clock anyway.
> But there's soc/pxa/corgi.c and soc/pxa/poodle.c that puzzle me.
> They seems to use a crystal, but they are setting a different sysclk
> depending on the rate.
> That seems wrong, but as I'm a newbie in ASoC...

Note that the CPU is clock master for those - it's going to be
outputting a clock based on the sample rate selected automatically.
These boards would be broken by your change as it stands.
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