@fubuntu
To Clarify
FP4 comes with anti rollback protection and it will only trigger if your bootloader is LOCKED.
If your bootloader is UNLOCKED, then anti rollback protection is ignored
From what you read in the /e/OS installation instructions
Caution: The FP4 comes with an anti-rollback feature. (...) If you try installing a version of /e/OS based on a security patch that is older than the one on your device, you will brick your device.
That is true if you try to relock your bootloader, as in the detail of /e/OS installation instructions caution section
- Rollback protection errors trigger if you install an update whose version number is LESS than the rollback index’s value stored on device.
- (...)
- Rollback protection errors are FATAL when the bootloader is LOCKED.
- Rollback protection errors are IGNORED when the bootloader is UNLOCKED.
In short, if you unlock your bootloader and downgrad your FP4, you won’t trigger anti-rollback protection as long as you don’t relock the bootloader.
Also, you cannot relock your bootloader with Ubuntu Touch installed anyway.
@Keneda It's safe to downgrae FP4 to FPOS11 as long as you don't relock your bootloader. My FP4 came with FPOS13 from the factory, and I successfully downgraded to FPOS11 and install Ubuntu Touch in April 2024. Just DON'T relock your bootloader, as the FP4 will reset get_unlock_ability
to 0 after the first FPOS11 boot. If you accidentally relock your bootloader with get_unlock_ability: 0
, then there is no way to unlock your bootloader again.
If you want to retain get_unlock_ability: 1
after the downgrade, just don't boot FPOS afterwards. (Source: https://forum.fairphone.com/t/how-do-i-obtain-get-unlock-ability-set-to-1-on-an-unlocked-fairphone-4/105018/4)