I've come across this EXT4 quirk while looking for clues about various EXT4 booting problems.
https://unix.stackexchange.com/questions/388432/what-does-this-mkfs-ext4-operand-mean
https://bugzilla.gnome.org/show_bug.cgi?id=766910
Basically, if you are experiencing booting EXT4 problem then make sure the the mkfs.ext4 that you use to format the partition do not use 64-bit option. For example, ^64bit indicated that the file system should be 32-bit.
mkfs.ext4 -O ^64bit -L roofs /dev/sdb1
This seems to be the new default set by a newer patch recently. Older u-boots have not caught up with this so it might cause problem.
-bodhi
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