Debug boot or network problem on Pioneer FreedomBox

My Pioneer-FreedomBox-HSK does not connect to the LAN after upgrading from Debian 10 to 11. At least, it did not start a DHCP client that my router would see. Not sure, if it does not boot or if there is a network problem. How can I debug and fix such a problem? Do I need a serial cable?

does not connect to the LAN after upgrading from Debian 10 to 11

Maybe I should have read that, before upgrading:

FreedomBox’s disk image for Pioneer hardware uses a patched u-boot to avoid this Ethernet problem. Are you using the OS shipped with the box or have you reinstalled vanilla Debian on it?

We have also tested that Pioneer hardware does not suffer the problem when using FreedomBox image for Bullseye. Could you please try this image perhaps on a new SD card while keeping the old SD card untouched?

Thanks @sunil for helping!
I probably overrode the freedombox packages with vanilla Debian ones.
Can I get the patched u-boot via a freedombox repository in my sources.list?
If so, which is the right “deb” line?

Is only u-boot relevant in respect to the Ethernet problem and the kernel version does not matter at all?

About the image: I unxz it and dd the image to /dev/something (the SD card), right?

It is not likely that you accidentally overwrote the u-boot. The u-boot part in discussion sits in a particular area outside of the filesystems. So, package upgrades could not cause this.

Any case, I assume you are able to get Bulleye image working properly. If so, take a full image backup of the SD card and then try the following to re-install u-boot:

dd if=u-boot-sunxi-with-spl.bin of=/dev/mmcblk0 bs=1k seek=8