cannot boot from microSD card on aarch64 machine

[Ricardo Wurmus <rekado@elephly.net>]

Hi,

I got myself a rockpro64 board.  I put armbian
(Armbian_21.08.1_Rockpro64_bullseye_current_5.10.60.img) on a microSD
card to check that it’s all working correctly.  Then I downloaded the
latest Guix System image for a pinebook pro and dd’d it to a USB drive.
With the armbian microSD card inserted (which contains an old version of
u-boot) I can boot from USB into Guix System.

So I then decided to build my own system and install a new u-boot onto
the microSD card.  Here’s the system I built:

--8<---------------cut here---------------start------------->8---
(operating-system
  (host-name "foo")
  (timezone "Europe/Berlin")
  (locale "en_US.utf8")
  (bootloader (bootloader-configuration
               (bootloader u-boot-rockpro64-rk3399-bootloader)
               ;; SD card/eMMC (SD priority) storage
               (target "/dev/mmcblk1")))
  (kernel linux-libre)
  (kernel-arguments
   (list "console=ttyS2")) ; UART2 connected on the Pi2 bus
  (file-systems (cons (file-system
                        (device "my-root")
                        (title 'label)
                        (mount-point "/")
                        (type "ext4"))
                      %base-file-systems))
  ...)
--8<---------------cut here---------------end--------------->8---

The actual system also has one more initrd module, which I can’t
remember now, but that shouldn’t matter.

I mounted the target disk (an SSD) at /mnt, made sure that the microSD
card was inserted, unmounted, and available at /dev/mmcblk1, and then
ran

   guix system init config.scm /mnt

This was successful.

Unfortunately, rebooting failed.  There is seemingly no activity at all
when I power on the board, so something’s not right with how u-boot was
installed on the microSD card.

Does it perhaps install the u-boot files at the wrong offsets?  How
would I begin to debug this?

I’d appreciate any hints.

-- 
Ricardo