[alsa-devel] Questions about ASoC driver implementation

[Matt Campbell]

Hi Lars,

Thanks for the information, that really clears things up for me! Having the
max9768 and lm4857 as examples should get me where I need to be.

~Matt

On Wed, Aug 12, 2015 at 11:14 AM, Lars-Peter Clausen <lars at metafoo.de>
wrote:

> Hi,
>
>
> On 08/12/2015 04:01 PM, Matt Campbell wrote:
> > Hi All,
> >
> > I'm diving into adding support for a new codec (AK4621) targeting IMX6
> SoC
> > and as this is my first dive into ALSA driver code (and first deep dive
> in
> > to Linux driver development) I've come up with a few questions. I've
> done a
> > lot of digging in available documentation as well as reading a lot of
> code,
> > but some things remain unclear.
> >
> > First, I'm a little confused with what appears to be inconsistent
> > terminology. The SoC overview.txt lists three types of component drivers:
> > codec, platform and machine. However, in the code there are four types of
> > snd_soc_register_* functions: card, platform, codec and component. From
> > looking at the underlying structs and how these are used in existing code
> > this is my best guess but please correct me if I'm wrong:
> >
> > codec -> snd_soc_register_codec
> > machine -> snd_soc_register_card
> > platform -> snd_soc_register_component and snd_soc_register_platform?
> (not
> > sure about this, from what I can gather at some point there was an API
> > switch to using component rather than platforms for the DAIs)
>
> There used to be a lot of similarity between platforms and CODECs and some
> code duplication. snd_soc_component was introduced is a new common base
> class for both CODEC and platform. It can also be used standalone if none
> of
> the platform or CODEC specific functionality is need.
>
> >
> > My second question is around adding support for an amplifier external to
> > the codec. The amplifier is a PGA controlled over SPI. One possible way I
> > can see to adding this is to create a SPI based codec driver for the PGA
> > that exposes an ALSA control for the gain level and give it a dummy DAI
> > then add it to the card as an aux_dev. This feels a little kludgy as the
> > PGA isn't a perfect fit for the codec class.
>
> You don't need to register a DAI with your CODEC it will work just fine
> without. Although in this case you don't need any CODEC specific features
> so
> the best is to just go with snd_soc_component. There are a few examples of
> snd_soc_component based drivers for external analog amplifiers, e.g.
> max9768
> or lm4857.
>
> - Lars
>