OK, kind of works. I started TWRP recovery and formatted all the device (removing encryption), then copied back the lineageOS (I used the last nightly, 2018-02-22) and addonsu zip files using a microUSB stick. Reinstalled everything. It works, the only annoying thing is that by formatting the sdcard I lost the backup I had previously done with TWRP of the original firmware, but that's fine, I was not planning of using it anyway.
- enabled USB debugging, root apps+ADB, enable third-party apps
- added F-Droid repo
- downloaded CryptFS from F-Droid
- Settings -> Security -> set up a temporary password for screen unlock
- Plugged in tablet, Settings -> Security -> encrypt device (using the temporary password above)
- reboot, this time seems to work (modulo the usual annoying "settings app has stopped working" one-time popup)
- changed encryption password with CryptFS (requires root of course)
- Settings -> Security -> changed screen unlock to a normal PIN
Everything seems to work so far: the device asks for the long decryption password at boot but only short PIN to unlock screen.
Planning to install WrongPINshutdown now, to complete anti-theft security setup.
So far so good, except ADB still doesn't work. Keeping a close eye on battery usage.
Coming next:
- testing whether TWRP can decrypt storage
- making sure at least LineageOS can mount USB drives... since MTP doesn't work it would be annoying having to use network or ADB to transfer large files...
---------- Post added at 01:17 PM ---------- Previous post was at 12:59 PM ----------
Babality!
- TWRP still cannot decrypt storage, does not even ask for the passphrase, just does not see the partition
- after trying the above, somehow the encrypted partition header got screwed: if I start Lineage OS, when I'm prompted for the passphrase. I always got "wrong password". Either using the "right" password, or using the old temporary password I used before, or the current device PIN, nothing: everything is "wrong password".
I'm reinstalling everything again and do a couple of final tests before giving up and forgetting about encryption.
I suspect this might be an issue of TWRP. I'm using version 3.0.2-0. I'm installing now the latest version (3.1.1-0) and see if things change.
Also, coming next MTP test.
---------- Post added at 01:37 PM ---------- Previous post was at 01:17 PM ----------
TWRP 3.1.1-0 bootloops tablet... I have to start from Odin again.
F**k all this s**t, my next device's gonna be an Apple :angryface: