Preliminary image for Raspberry Pi 4

[Lucas Nussbaum <lucas@debian.org>]

( Ccing debian-arm for info )

Hi Gunnar,

I (finally) wrapped up my work on building an RPI4 image. You will find
a suitable raspi_4.yaml file in
https://salsa.debian.org/raspi-team/image-specs/-/blob/rpi4/raspi_4.yaml

I did not try merging it into the raspi_*.yaml generation script yet. I
don't think it's that useful at this point.

It uses the 5.5 kernel from unstable, so only stuff that is listed as
working in 5.5 on https://github.com/lategoodbye/rpi-zero/issues/43 will
work. Most notably, USB does not work.

I think that it could be added in its current state to
https://raspi.debian.net/ (I don't see any point in delaying this; early
testing would be great).

I tested the image on the 2GB and 4GB variants.

The main next step is to switch to linux 5.6, once it gets into
experimental (it was uploaded but failed to build, see
https://buildd.debian.org/status/logs.php?pkg=linux&arch=arm64 ).

It would also be nice to use raspi-firmware and linux from
buster-backports once both are backported, but that's not a big issue
(pinning from unstable/experimental is probably fine for the time being).


I also did some work on booting with u-boot. See
https://salsa.debian.org/raspi-team/image-specs/-/blob/rpi4-wip/raspi_4.linux5.6_uboot.yaml
This ended up not being necessary for the RPI4, but I wonder if we
should switch to booting with u-boot for all images.

I also noticed that you don't seem to use virt-sparsify (from
libguestfs-tools) to make the images smaller. It seems to save about 10%
off the .img.xz file.


My notes are on https://wiki.debian.org/RaspberryPi4

Lucas