So, I've done some first tests and I can confirm the following:

Thinkpad T440p / Debian 10 / R 14.0.9 (Development) /  kmilo-trinity & legacy
HDA Intel PCH

FN - F1/F2/F3:  mute on/off is shown, but no effect
		Sound 100& / 90% appears but no effect
There are some problems with HDA Intel PCH and HDMI: some time kmix tries to 
control HDMI so HDA Intel PCH does not react.




Thinkpad X220 Tablet / Debian 9 / R 14.0.5 (Development)
kmilo-trinity & legacy

Fn-Home / Fn-End work (screen backlight)
Fn- sound keys (play, stop, etc...) don't work
Sound +/- button (physical) work
Mute button mutes but does not unmute. It does print "unmute" on screen, but I 
need to use kmixer to get sound back.



Thinkpad T400 / Debian 9 / R 14.0.8 /kmilo-trinity & Legacy

Fn-Home / Fn-End work (screen backlight)
Fn- sound keys (play, stop, etc...) don't work
Sound +/- button (physical) work
Mute button mutes but does not unmute. It does print "unmute" on screen and 
kmimx icon shows mute, but I need to use kmixer to get sound back.

I did not test other buttons.

Thierry