Systemd-boot not properly loading device tree, when loaded by U-boot (ARM64, tested on RK3399)

[Qu Wenruo]

Hi,

I'm recently testing booting my RK3399 boards with the following boot
sequence:

U-boot -> systemd-boot (EFI payload) -> kernel

Which provides much more flex than plain extlinux conf from U-boot.
(More choice, easier to write config, runtime kernel change).

So far "kernel" and "initramfs" key work fine.

But I notice that "devicetree" key is not working properly.

The Uboot fdt search path doesn't include "/dtbs" which is used by my
distro, and my entry config specify the device-tree file like this:

title        ManjaroARM boot from nvme
linux        /Image
devicetree    /dtbs/rockchip/rk3399-rockpro64.dtb
initrd        /initramfs-linux.img
options        console=ttyS2,1500000 root=/dev/arm_nvme/root rw loglevel=7

Thus if systemd-boot doesn't load the correct device-tree, kernel will
use the default fdt passed from Uboot, which is already out-of-date and
can cause problems for the upstream kernel I used.

Unfortunately, with above config, after booting the kernel, the fdt is
the fallback one from Uboot, not loading the proper one specified by
systemd-boot config.

The proof I went is checking the opp table.
I have replaced the "/dtbs/rockchip/rk3399-rockpro64.dtb" with a custom
dtb which uses op1 tables.
But the kernel only sees a very out-of-dated fdt, which some opp is even
invalid.

How could I continue debugging the missing link?
Like what systemd-boot needs to load the device-tree? Or U-boot EFI
environment lacks certain facility to support systemd-boot?

Thanks,
Qu