hi @tba, there is no DB820c forum since the board is not launched yet, and users can’t (easily) get one yet.
for now , no bootloaders are distributed by QCOM for DB820c, nor Linaro. You have to get the bootloaders from ‘whoever get you the board in the first place’. This will of course change once the board is more officially available.
the Linux builds (OE, Debian, …) should work with the bootloader that you have on your board (e.g. from Android). the most notable difference is that there is no ‘rootfs’ partition (e.g. no specific GPT for Linux), but you can use ‘userdata’ or ‘system’ partitions from Android to flash the Linux root fs image.