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

[Takashi Iwai]

On Fri, 29 Jul 2016 18:07:02 +0200,
Vinod Koul wrote:
> 
> On Fri, Jul 29, 2016 at 11:07:49AM +0200, Lars-Peter Clausen wrote:
> > 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.
> 
> That still seems a bit fancy hardware :)
> 
> If we can reasonably support this, I am for it. But not making stuff
> overtly complex...

Yes, we don't have to overreact to a dream immediately now.
We should consider whether it can be shifted to the card-level instead
before worrying too much about hot-unplug of an ASoC component.  Then
the whole story becomes far easier.

And, the suppress_bind_attrs flag I suggested is only to suppress the
sysfs bind/unbind, and doesn't mean to prohibit hotplug itself via the
bus driver.


Takashi