Linux on Elitebook X360

[digikey]

Hello,
I recently got my Elitebook X360 1040 G5 and started using Linux on it. Here's my experience so far:

Most of the hardware is working flawless:

• Wifi+Bluetooth+Speakers
• Touchscreen and touchpad including multitouch gestures and the rotation sensor work out of the box
• Pen support and pressure sensitivty is there
• The Sure View switch seems to be hardware controlled and works
• The webcam is recognized as two seperate ones:
  • "normal" color web cam works
  • IR web cam shows flashing, greyish pictures only

Now the things that don't work for me right now:

• The internal microphone is not recognized
  • plugging in a headset and using its external microphone works
  • There is some recent development regarding the newer Intel microphones:
    https://bugzilla.kernel.org/show_bug.cgi?id=201251
• The microphone mute key and its LED don't work
• The Intel LTE modem is not recognized and propably never will, since there's no support from either Intel or HP:
  https://mobile.twitter.com/intel/status/981701464040136705
• With Sure View turned off: The display brigthness can be controlled through software, but not with the keyboard hotkeys
• With Sure View tuned on: The display brightness can be controlled with the keyboard hotkeys, but not through software
• The calendar, screen, answer and hang-up phone keys produce an invalid key code, I was able to map them by taking a look at dmesg and using "setkeycodes 66 5" etc.
  • They are producing multiple key presses (Ctrl+Shift+4)

Who's also using Linux on their Elitebook and what's your experience like?

Any idea on how to get the microphone working?