Thanks for all the great work on making those images available!
I do have a couple of questions though. I'm using the 5.86 ubuntu image for s9xx, and it seems like I cannot run fstrim on the mounted mmcblk1 device. Attempting to fstrim the root partition (which resides on the emmc) will result in a "the discard operation is not supported" error. Is this a dtb issue, or it's simply not supported by the mainline kernel at this time? The box is Phicomm N1 (s905d) running with the included dtb file in the image if it matters.
Also, could you tell me how the bootable kernel image (zImage located in /boot) was generated? I tried to compile the mainline kernel with the config file in your github repository and it won't even boot, because u-boot complains about a bad magic (which I believe is the "0x41524d64" located at 0x38 of the "zImage" file?). The "vmlinuz" file that I compiled has an ELF magic at the very beginning, and the "0x41524d64" magic at 0x38 wasn't there. I'd really appreciate some tips on this as I'm having a hard time finding more info about this matter.