TL;DR: All the crazy bootloader shit that affected 32 bit ARM infects 64 bit ARM too.
I pretty much followed Robert Gadsdon’s instructions here, except I had to compile mkbootimg by hand from the CyanogenMod sources as it doesn’t seem to be available in Fedora.
Luckily I have all the bits you need to attach a USB serial port:
U-boot was installed as the bootloader as above.
For the disk image, I started with the virt-builder Fedora 23 aarch64 image. I copied this image to the SD card by doing:
virt-builder --arch aarch64 fedora-23 --output /dev/mmcblkX
I didn’t expect this would boot, because the kernel is wrong, and the u-boot I flashed to the Dragonboard is in any case looking for a different file. So I cross-compiled a kernel by following the Linaro instructions here (only up to the make Image step).
I didn’t manage to get the kernel to boot, because it just doesn’t load. Or maybe it does load but doesn’t find the serial port. Whatever.
Richard WM Jones 
Re: All the crazy bootloader shit that affected 32 bit ARM infects 64 bit ARM too.
Not if your platform conforms to the Server Base Boot Requirements (SBBR) 🙂
Yeah, it’s all a real shame that nothing is standardized on these cheap dev boards.
rpms and images at https://www.kraxel.org/repos/qcom/
(didn’t try u-boot, boot partition carries linux kernel image).
These boards are the beginning and developers are using them to build standard comforting of software. At that’s the current state. It’s gonna take time before things are correct, before they upstreamed and before these boards are released with pieces working according to the standard. The idea was to get hardware out so that developers can work on it.
They’re going about it the wrong way. Android forks Linux and doesn’t upstream very much, and the ARM partners write crap drivers that can’t ever be upstreamed. I don’t see how any improvement is possible until that process is fixed.
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