Hi again,
after browsing some discussion forums, I think I have found a solution for the non-persistent calibration values.
As I understand it, there are two interface layers for touch screen devices, evdev (older) and libinput (newer, but also uses evdev). The calibration procedure (calib, xinput_calibrator) relies on evdev and thus there can be cases where the calibration is in conflict with libinput.
Here is what I did to make it work, i.e. to make changes persistent. It survives reboot and software update.
ssh -X root@yourraspberry
apt-get install xserver-xorg-input-evdev
apt-get install xinput-calibrator
export DISPLAY=:0.0
xinput set-prop “ADS7846 Touchscreen” ‘Coordinate Transformation Matrix’ -1 0 1 0 -1 1 0 0 1
Do the actual calibration:
xinput_calibrator
Rename 10-evdev.conf in /usr/share/X11/xorg.conf.d/ such that it is executed after 40-libinput.conf
mv /usr/share/X11/xorg.conf.d/10-evdev.conf /usr/share/X11/xorg.conf.d/45-evdev.conf
Open 45-evdev.conf and add the two lines from the output of the xinput_calibrator at the section which has “evdev touchscreen catchall” in it.
These are values that work fine for my touchscreen:
Section "InputClass"
Identifier "evdev touchscreen catchall"
MatchIsTouchscreen "on"
MatchDevicePath "/dev/input/event*"
Driver "evdev"
#Custom Options below
Option "Calibration" "135 3804 207 3867"
Option "SwapAxes" "0"
EndSection
Additionally, rename any (calibration.)conf file in \etc\X11\xorg.conf.d\ to *.conf~.
Also, deactivate 98-screen-calibration.conf in \usr\share\X11\xorg.conf.d\ by renaming conf to conf~ (or whatever you prefer).
I have tested it on my zynthian (image from 2020-05-25) where I already tried some other attempts described in this thread. Could someone confirm if it works with a fresh image?
Good luck 