Just gave this a whirl, changing nixos/modules/system/boot/loader/raspberrypi/uboot-builder.{nix,sh} to accommodate it. Unfortunately, I got stuck at the rainbow boot screen, so I cannot confirm this working.

Hmm, there's changes missing for an sd-image to work. Though I won't have the time to do that until after NixCon.

• nixpkgs/nixos/modules/installer/cd-dvd/sd-image-aarch64.nix

  Lines 52 to 55 in dd05027

  	in ''
  	(cd ${pkgs.raspberrypifw}/share/raspberrypi/boot && cp bootcode.bin fixup*.dat start*.elf $NIX_BUILD_TOP/firmware/)
  	cp ${pkgs.ubootRaspberryPi3_64bit}/u-boot.bin firmware/u-boot-rpi3.bin
  	cp ${configTxt} firmware/config.txt

Around there the u-boot for raspberry 4 will need to be copied, and config.txt will need to be extended to configure per-generation around here:

• nixpkgs/nixos/modules/installer/cd-dvd/sd-image-aarch64.nix

  Line 39 in dd05027

  kernel=u-boot-rpi3.bin

Once done, a build of the generic sd image, with the generic latest kernel, and hopefully it works.

I deployed straight to my running machine with nixops, fortunately making a backup of /boot beforehand. I'll try an sd card image later.

This is blocked until there is a bcm2711-rpi-4-b.dts from mainline.

With the current state of this branch, adding a bcm2711-rpi-4-b.dtb to the root of the FIRMWARE partition of the sd_image will make u-boot successfully boot. Though, since mainline kernel does not yet have the rpi 4 device tree, it fails to continue booting.

This might be a bigger issue since it's looking like the next LTS (5.4) will not have rpi 4 support. In this situation, building the firmware partition may differ depending on the kernel it is built with. Or, alternatively, depend on a mainline latest kernel build in addition to last LTS. Or, final alternative, is that u-boot imports the kernel device trees (as they usually do) with an rpi-4 dts, and then everything is fine and self-contained.

With the current state of this branch, adding a bcm2711-rpi-4-b.dtb to the root of the FIRMWARE partition of the sd_image will make u-boot successfully boot.

yes, u-boot starts up fine.

Though, since mainline kernel does not yet have the rpi 4 device tree, it fails to continue booting.

And there i'm stuck on 'Starting kernel...` (extlinux.conf is read alright).
So that must be why i got stuck here.

Here's an issue tracking the mainlining efforts.

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Still desired, still blocked.

@samueldr Would this not work with pkgs.linuxPackages_rpi4 ?
Edit: seems like it doesn't...

AFAICT this has been superseded by #97883 so closing - please reopen if this if I missed something and this is still desired as a separate PR.