[alsa-devel] No audio on iMac18,1 (A1418) with kernel 4.15.14

[Andrey L]

Good day. I'm yet another owner of 2018 iMac who can't get sound to 
work. I was wondering if someone with the expertise can comment whether 
it is possible at all. Relevant earlier threads:

https://www.spinics.net/lists/alsa-devel/msg76308.html

https://bbs.archlinux.org/viewtopic.php?id=233449

Like others before I tried pretty much all options of snd-hda-intel with 
no success. The sound however works on windows, so I decided to look 
there. The codec chip is Cirrus CS4208, and without installing chip 
drivers, there was no audio in windows as well. It turns out that 
windows driver is a generic chip driver, where all hardware 
configuration is stored in registry (binary config file). These settings 
are configured in installation inf file (text config file) , and what is 
important – they are heavily commented.

Unfortunately I do lack domain knowledge about hda-intel / codec / 
endpoint or alsa architecture, nor have I any desire to learn this area. 
I would appreciate if anyone can look at my findings and tell whether 
current linux drivers can be hacked to support this configuration.

I’ve copied and sorted all relevant sections from inf file here - 
https://pastebin.com/p74qSdzc

Here is what INF file defines:

The chip is CS4208, but it is also referenced as "Cirrus Logic CS8409 
(AB 16)" .

There are 4 interfaces: speaker, headphones, mic and d-mic.

Headphones are stereo. Speakers are quad(!!!) “quad (FL/FR - woofers, 
RL/RR – tweeters)”.


The INF file contains following sections:

CONF_0910.InitVerbs – apparently configuration initialization sequence, 
lists register-value pairs written by driver at startup.

SettingsCS8409Exit – same for shutdown


CONF_0900.Gpio, CONF_0910.Gpio – configuration of GPIO with comments


CONF_0900.TXRX – Widgets,pins and amps caps (I have no clue what it is), 
but from comments this section seems to define all chip connections.


CONF_09xx.I2C – raw i2c commands for various scenarios (chip power up, 
start/stop streaming, etc).


So the question is, is this data of any help? Can this be somehow 
plugged into existing hda-intel or cs4207 drivers to get the sound?


Thanks.