Today I don't have much time to analize, but i've found some interesting sources.
There are no userspace applications communicating over the i2c except for csd. Only the kernel modules.

Sources:
For cover switch (toh-event):
https://github.com/KonstaT/sailfisho...sc/toh-event.c
This module loads toh-core on cover key event.

For eeprom (toh-core):
https://github.com/KonstaT/sailfisho...vers/mfd/toh.c

If an eeprom with valid data is present, toh will appear in /sys fs.

From toh-core source eeprom data structure format can be extracted and than tested.


Looking at /boot/config*, it looks like support for TCA8418 is not enabled. (I didn't check if it is compatible with 8424).

Maybe an plugin like the /usr/lib/tohd/tohd-plugin-nfc-nxp.so has to be written.