>> Coreboot did work well, but froze sometimes when booting during the
>> assigning resources step (more or less exactly after assigning the PCI
>> 14.3 or PNP 002e.2 device, which happen to be close to each other inside
>> the devicetree). I had to remove the power cord in order to be able to
>> boot again (or to get the next random freeze...). Rarely, after such an
>> recovery, I have got flooded by IOMMU warnings in Linux which would only
>> disappear after another reboot.
>
> Ah, that resume reboot-loop issue. The bit that tells to do S3 resume
> is a sticky register backed up by Vstb rail. With [2] you should not
> need to do full power-cycling at least. We should extend this work to
> other platforms.
>

I am not sure whether the term resume reboot-loop applies for my issue
(side note: I used a serial connection to monitor the boot process):

Rebooting (via holding the power button for some seconds) after
encountering a freeze (aka stopping at the assign resource step)
resulted into having no output from serial at all. I could repeat this
with no effect at all, the computer seemed to be dead. Only removing the
power cord could solve the issue.

This issue could occur when rebooting but even when cold booting.

Answers are inside the text.
I forgot to mention that I am currently on commit 793ae846e8.