[alsa-devel] ASoC: Device tree binding to dummy codec

[Mark Brown]

On Mon, Jul 28, 2014 at 08:54:13AM -0400, jonsmirl at gmail.com wrote:
> On Mon, Jul 28, 2014 at 7:20 AM, Mark Brown <broonie at kernel.org> wrote:
> > On Mon, Jul 28, 2014 at 08:24:39AM +0200, Lars-Peter Clausen wrote:
> >> Cc ASoC maintainers.

> > Jon, you should really know to CC maintainers.

> Are the all CC'd now? I thought the ALSA list was sufficient.

No, you should always CC maintainers - never assume anything sent only
to a mailing list is going to be seen or read, certainly not with any
degree of promptness.

> on-chip codec - it is ADC/DAC with FIFIO directly attached. There is
> no separate bus. on-chip codec supports things like mic1, mic2, line
> in, line out, hp out. Most boards populate only a subset of the jacks.
> Right now the device driver makes a dummy codec and internally creates
> a card and links everything together.

> http://git.elopez.com.ar/linux/src/abc050fbbaa5302b76ac585954cd207961fc9159/sound/soc/sunxi/sunxi-codec.c?at=sunxi-codec

> Then someone came along and wanted to add a MAX9768. We're stuck
> because the way the driver is built it doesn't support the external
> MAX9768 codec driver.  MAX9768 is just an amp with I2C control of
> volume.

This doesn't seem hard - just extend the binding for the device/card to
allow auxiliary devices to be specified (the matching code supports
that).

> So how should the device tree look for no external amp? Right now
> there is just a device node and the driver makes a card/dummy-codec
> internally.

Your CODEC shouldn't be a completely dummy one, at a minimum it has some
external pins which need to be described and documented.

> How should the device tree look when there is an external amp?  Maybe
> this amp should just be a chip of the device node?

Just the same as any other card - allow a phandle to be provided to the
amplifier.

> How should the various jack populations be handled in the device tree?

Assuming "jack populations" are DAPM links just do it the same way as
anything else and use snd_soc_of_parse_audio_routing().
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