Hi everyone.
I'm struggling for more than one month, fighting to make the touchpad works on x1carbon 8th gen with Debian stretch. Yes stretch, it means the lastest kernel I can work on is 4.19 (backports)
The touchpad is not recognized in /proc/bus/input/devices
This is the output of the xinput:
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ PS/2 Generic Mouse id=12 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)]
↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)]
↳ Power Button id=6 [slave keyboard (3)]
↳ Sleep Button id=7 [slave keyboard (3)]
↳ Lenovo ThinkPad USB-C Dock Gen2 USB Audio id=8 [slave keyboard (3)]
↳ Integrated Camera: Integrated C id=9 [slave keyboard (3)]
↳ Intel HID events id=10 [slave keyboard (3)]
↳ AT Translated Set 2 keyboard id=11 [slave keyboard (3)]
↳ ThinkPad Extra Buttons id=13 [slave keyboard (3)]
but the lsusb I can find some information:
Bus 001 Device 004: ID 06cb:00bd Synaptics, Inc.

If I boot using ubuntu live everything is ok with kernel 5.8 and xinput identify this:
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ SYNA8006:00 06CB:CD8B Mouse id=10 [slave pointer (2)]
⎜ ↳ SYNA8006:00 06CB:CD8B Touchpad id=11 [slave pointer (2)]
⎜ ↳ TPPS/2 Elan TrackPoint id=15 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)]
↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)]
↳ Power Button id=6 [slave keyboard (3)]
↳ Video Bus id=7 [slave keyboard (3)]
↳ Sleep Button id=8 [slave keyboard (3)]
↳ Integrated Camera: Integrated C id=9 [slave keyboard (3)]
↳ sof-hda-dsp Headset Jack id=12 [slave keyboard (3)]
↳ Intel HID events id=13 [slave keyboard (3)]
↳ AT Translated Set 2 keyboard id=14 [slave keyboard (3)]
↳ ThinkPad Extra Buttons id=16 [slave keyboard (3)]

I have tried everything, kernel parameters, changed between synaptcs and libinput drivers, change re-compile kernel with some i2c parameters. No luck so far. Go to buster or another Linux OS with a new kernel is not an option. I tried the solutions I found for SYNA8004:00 and it has failed. Does anyone have an idea?

Which specific version of 4.19? Since X1 Carbon (8th Gen) was announced in January 2020 I would guess you'd need at least 4.19.93 for any new drivers it needs, and potentially a later version.

Why is Buster not an option? At a minimum, live booting Buster on 4.19 kernel should give you a smaller set of differences to compare against than Ubuntu with 5.8 kernel.

The Arch wiki has an X1 Carbon page and mentions modules psmouse, rmi_smbus and i2c_i801 for the touchpad - can you use modprobe to verify all three of those are loaded?

Hi boughtonp, thank you for your reply. Currently, I have the kernel 4.19.155. The company software running very stable in the Debian stretch, that's why they are postponed as much as possible an upgrade. I already tried modprobe psmouse, rmi_smbus and i2c_i801. the i2c_i801 is in use for Trackpoint. The Trackpoint is working.

I'm going to guess it probably isn't going to work simpmly due to the age of the distro, but are you using synaptics drivers or libinput? I'd guess libinput would have a BETTER chance at functionality.

https://github.com/fwupd/fwupd/wiki/LVFS-Testing-remote

The simple answer is to use a modern distro I'd think. There are tons of web pages on this issue starting in 2019 and many point to the firmware. If you insist on running an older kernel then you will have to fix driver and firmware. I doubt it will be updated by disto. Kernel is new enough I think to move forward with long way around patch.

Hi guys, I have a workaround. The liquorix project has several kernels replacement built. I found the kernel 5.9 for the Debian stretch. I installed it and the touchpad is working. The solution was accepted here, so I will change it as solved. Thank you guys for your time.