[Sound-open-firmware] [PATCH 1/2] uapi: ipc: Add lbm in sof_ipc_dai_config

[Liam Girdwood]

On Mon, 2018-06-04 at 10:08 -0500, Pierre-Louis Bossart wrote:
> > > > 
> > > > loopback is not tied to HW config, it can be enabled/disable at runtime
> > > > so
> > > > hould use the standard IPC for component commands like volume.
> > > 
> > > OK, this is done by suggestion from Pierre to not use a kcontrol but a
> > > static topology token,
> > > So if it is need to be runtime enable/disable. Then a kcontrol or a
> > > debugfs should be used?
> > 
> > kcontrol is more flexible since we don't have to change topologies and they
> > should come as standard with all SSP topologies.
> 
> I don't really agree here. If a user sets the loopback kcontrol there's 
> no audio any more. "Be careful what you wish for" seems to apply here, 
> this will generate support issues. 

We've had this in ALSA/ASoC with the codecs for some while now so most users
will do a alsactl or UCM file with good settings. I know it's very easy to
change the route with alsamixer/amixer and mute the output, but I think adding
one more here probably wont matter that much.

> LBM is only useful in test modes, and 
> there's no problem generating test configurations.

LBM is very useful for debug/integration usages and it's easier/quicker to ask a
user to enable the LBM kcontrol as a test than to modify their topology or use
the test topology (which may not be valid for them).

Liam