[...]
>>> +
>>> &blsp_i2c2 {
>>> status = "okay";
>>>
>>> @@ -243,6 +258,13 @@ &gpu {
>>> status = "okay";
>>> };
>>>
>>> +&lpass {
>>> + dai-link@3 {
>>> + reg = <MI2S_QUATERNARY>;
>>> + qcom,playback-sd-lines = <1>;
>>> + };
>>> +};
>> Is that not status = reserved?
>>
>
> Correct. This is here to simplify switching to the modem-bypass audio
> routing if someone does not need (or want) the modem. The direct audio
> path with the LPASS drivers tends to be more reliable and configurable
> (especially wrt bit formats, sampling rates, latency, channels etc).
> I know that at some point this helped someone who tried to use an old
> phone as some kind of portable musical instrument / synthesizer.
>
> It's not too obvious that these definitions would be needed when making
> those changes (because devices using the standard SD lines (i.e <0>) do
> not need it). If you forget about this you get non-functional audio with
> no error or any hint what could be wrong.
>
> To simplify switching between the different audio routing options, the
> lk2nd bootloader actually has an option to do this transformation in the
> DTB automagically during boot. It's sort of like a DTB overlay that
> disables the QDSP6 audio path and enables this node instead. The DAI
> links are also adjusted where necessary.
>
> Do you think a comment would help here?
I'd say a comment would be necessary here :D
While I understand this use-case, I believe this is better suited
for an actual DTBO or something entirely kept inside lk2nd.
Otherwise this looks very confusing to an outside reader.
Konrad
