[alsa-devel] [PATCH 1/2] ASoC: tlv320aic32x4: Add Switch for Setting Common Mode Voltage

[Annaliese McDermond]

> On Apr 3, 2019, at 10:43 PM, Mark Brown <broonie at kernel.org> wrote:
> 
>> On Wed, Apr 03, 2019 at 09:01:54PM -0700, Annaliese McDermond wrote:
>> Add a switch for setting common mode voltage.  This can allow
>> for higher drive levels on the amplifier outputs.
> 
> Should this be runtime controllable or is this something that's likely
> to be fixed by the board design?

For us, in our particular application, it’s really necessary at runtime. Our use
case is not that we are driving speakers, but the inputs of various amateur 
radio units. Experience has shown us that the input characteristics of these 
devices vary widely and require different levels of drive to function 
correctly; a Motorola may need a lot of drive compared to an Icom that 
requires almost none. 

We could modify the board to have an outboard amplifier of some sort on 
it, but that just moves the problem to another component.   Or we could put 
some sort of prescaling switchable resistors in the board, but this also adds 
complexity that’s dubious. 

I’ve thought about putting these in the DT, but it occurs to me that they are 
really not board design dependent. The options are really there to control 
power consumption on the chip. In our application that’s really not important. 
For other applications I can see where that might be useful to change 
dynamically at runtime depending on current conditions. 

—
Annaliese McDermond
nh6z at nh6z.net