[alsa-devel] Question about struct snd_soc_dai() :: cpu_dai->codec

[Lars-Peter Clausen]

On 07/29/2016 02:30 AM, Takashi Sakamoto wrote:
> Lars,
> 
> On Jul 29 2016 05:33, Lars-Peter Clausen wrote:
>> Hotplug is something that always pops up sooner or later. E.g. if someone
>> puts a ASoC supported CODEC on a hot-pluggable device (maybe USB) we
>> don't want to duplicate the code, but be able to reuse.
> 
> (A bit to sidetrack)
> 
> To me, it's unclear for devices on USB. When ALSA SoC part supports these
> devices, what is the scenario you assumed? In short, assuming we put codes
> to ALSA SoC part, what is the shape of the corresponding devices and links
> of pairs of endpoints? Additionally, in this case, what codes are able to be
> reused?

Lets say you have USB stick with a small micro controller or FPGA which has
a USB interface on one side and a I2S and I2C interface on the other side.
The I2S and I2C are connected to a CODEC. I2S for data, I2C for control. If
the interface is implemented in a way so that it is just a simple USB to I2C
bridge, this means the raw I2C commands are send over the USB interface you
can implement a I2C adapter driver for this bridge. If you have that you can
instantiate the existing ASoC CODEC driver, which is a I2C device driver, on
the bus registered by the adapter.

- Lars