[alsa-devel] Configure a CODEC which has I2C connected to CPU, but no PCM bus connection

Mark Brown broonie at kernel.org
Mon Apr 29 22:33:55 CEST 2013

On Tue, Feb 26, 2013 at 12:01:02AM +0000, Craig McQueen wrote:

Always CC maintainers on posts, if you just mail the list your message
is likely to be lost in the noise.  Also please fix your MUA to word wrap
within paragraphs for legibility.

> I have an embedded device with somewhat unusual configuration: there
> is a second audio CODEC (Wolfson WM8940) which is connected to the PCM
> interface of another device (a radio module, which is acting as PCM
> bus master), so that radio device can do analog audio I/O. So there is
> no CPU<-->CODEC PCM link, but the CODEC _is_ connected to the CPU's
> I2C, and the CPU needs to configure the CODEC registers to interface
> to the radio module.

That's fairly normal - most mobile phones do this.  Take a look at the
neo1973, speyside or bells drivers for example of such a configuration.
You can just connect two CODEC DAIs directly together and either start
the audio from the application layer by running through all the steps
for streaming except for actually starting DMA like:


does or supply a configuration in the machine driver (if the format is
fixed) like speyside and bells do.
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