dapm, device tree, clock control - questions

[Eliot Blennerhassett]

Hello again,

I got no answers last time I posted this

So, the meta-questions are
* Should I be asking somewhere else?
* Should I be reading something else to find my answers?
* Is there a better way to ask these questions?

thanks

On 21/10/20 10:50 pm, Eliot Blennerhassett wrote:
> Greetings,
> 
> First the basic questions, so you can quickly stop reading if this is
> not your thing.  Background details follow. Specific answers, or
> pointers to relevant reading both appreciated.
> 
> 1) How do I force a DAI clock to keep running even when no audio is
> streaming? Can I do this with DT, or some runtime switch?  OR how do I
> disable dapm so everything is powered on all the time?
> 
> 2) Two devices: one DAC, one dumb digital audio transmitter both
> connected to same serial audio data - how to model the second one in DT
> (or not)? it has some settings needed after clock starts, must keep
> clock running.

> I have host CPU imx8mm
>               
> DAI is sound/soc/fsl/fsl_sai.c
> 
> The codec is sound/soc/codecs/ak4458.c
> 
> The digital audio transmitter is CS8406 (no driver yet?).
> 
> Both the above are connected to the same DAI signals (MCLK, TXC, TXFS, TXD)

--------.
imx8mm  |
        |
    SAI *======+======[ ak4458 ]
        |      I      [        ]->Line_Out
   I2C2 *------I--+---[        ]
--------'      I  |
               I  `---[ cs8406 ]
               "======[        ]->iec958_out


> CS8406 needs MCLK before it can be configured, and loses config if clock
> stops.  Currently it is configured via I2C from userspace, but this is
> completely unaware of stream stop/start.  Is there a way to hook into
> stream state events so that this setup can be done after the MCLK starts
> before audio starts?
> 
> I desire for no discontinuity in analog or digital outputs as streams
> stop and start.
> 
> I have read
> Documentation/sound/soc/dapm.rst and its brothers.
> Documentation/devicetree/*
> is there elsewhere I should read to get a newbies intro to this stuff?
> 
> It must be about 8 years since I did any ALSA development, and then I
> wasn't in the ASoC space, so quite a learning curve here.
> 
> many thanks
> 


-- 
Eliot