Lenovo m720s combined audio jack not working (ALC233)

Hey,

The front audio jack on my newly purchased (but not new) Lenovo m720s doesn't make a microphone output appear in PulseAudio when a headset is plugged in. The headphone part works correctly though. The "sof-hda-dsp Front Headphone" evdev device will switch the state of SW_HEADPHONE_INSERT as expected.

Does anyone know whether the headphones/headset switching is supposed to be automatic, or would that trigger a "what did you plug in" dialogue as on some Dell machines I've worked with?

I couldn't find any quirks in sound/pci/hda that would be directly related to this problem (eg. Lenovo, ALC233 and mic presence), so I'm a bit stumped.

I've attached the pinout information from alsa-info.

Any ideas?

Cheers