For me, here is what was missing in the documentation :
It should be explained that the user has to “unlock OEM” before trying to flash the recovery. Else you have the red error message “Custom Binary (RECOVERY) blocked By OEM Lock” after flashing it, and you still have the original recovery (that refuses to use the /e/ adb files)
There are several steps :
- start the tablet with original Android, run system update to have the latest ROM
- go to settings and unlock developer mode, by tapping 10 times on the version number
- a new “developer settings” menu should appear, where you have to check “Unlock OEM”
- then you need to restart in download mode : turn off the device (long press on volume down + power), unplug it, press both volume up and down, keep them and plug the cable
- a screen asks you to confirm with volume up OR to unlock the device with a long volume up press : that’s what you need to do (long press on “volume up”) then confirm all the warning messages
- the tablet data will be reset and it will reboot. If you enable and enter developer settings again, the “Unlock OEM” should be grey and saying that the bootloader is already unlocked
- then you can go to download mode again, and run the heimdall/odin command to flash the recovery
- when it’s finished, the tablet is still in download mode. Check that you don’t have the red message “Custom Binary (RECOVERY) blocked By OEM Lock”. The current documentation says to reboot it but it’s tricky to rebooting it in recovery mode : you have to press power + volume down for ~7s, release these buttons immediately when the screen goes blank, and immediately press power + volume up instead
- you should then be in /e/ recovery. You should see the /e/ logo
- then you can follow the current documentation to adb sideload the image etc
On each startup, the tablet displays a big warning, but afterwards it seems to work fine (I did not test a lot, yet)