https://kernel.googlesource.com/pub/scm/linux/kernel/git/cjb/mmc-utils/+/7bd1320b2cb38f040ab5cf017d17e283496690bf
# echo 0 > /sys/block/mmcblk1boot1/force_ro
ext csd
PARTITION_CONFIG (formerly BOOT_CONFIG)
http://rere.qmqm.pl/~mirq/JESD84-A44.pdf