[alsa-devel] HDA Intel ALC889A optical spdif input on MacBooks

[René Rebe]

Hi,

recently I wanted to connect my low noise mic pre-amp via optical spdif to a spare "10 year” old MacBook or MacBookPro.
Those indeed have a optical input in the 3.5mm headphone jack. On macOS this also works and works as expected.

On Linux, however, no matter what I do I only get zeros when recording the -D iec958.

In /proc I see 3 capture sub-devices, where the 2nd is labeled:

# cat /proc/asound/card0/pcm1c/info 
...
id: ALC889A Digital
name: ALC889A Digital
...

The behavior is the same on booth the MacBook as well as the MacBook Pro with either of those PCI devices:

00:1b.0 Audio device: Intel Corporation 82801G (ICH7 Family) High Definition Audio Controller (rev 02)
00:1b.0 Audio device: Intel Corporation 82801H (ICH8 Family) HD Audio Controller (rev 03)

I have the feeling there could be some auto sensing be involved, as in the macOS system preferences I see the input switching from Mic to Optical Input as soon as I plugin in an active fibre.

As I’m not familiar with this Intel HD stuff, any hint how to start analyzing and poking this mystery would be highly appreciated.

Best regards,
	René

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