cc @dezgeg

@lopsided98 if I wanted to try this pr on my pi how would I go about doing it?

@mogorman Add boot.kernelPackages = pkgs.linuxPackages_rpi; to your config and then run nixos-rebuild -I nixpkgs=/path/to/nixpkgs switch where /path/to/nixpkgs is the nixpkgs git repo with this branch checked out.

Ah, I didn't know they support this configuration.

@lopsided98 How about writing the DTB conditionals like this though: dezgeg@f3ac96a? Can you runtime-test that one? At least it builds for me (after rebasing on top of the latest linux-rpi update I did so that it doesn't fail on bcm2710-rpi-cm3.dtb).

@dezgeg Your patch boots correctly for me.

@lopsided98 thanks that booted for me. I did have a question if you know how to resolve. I am trying to get my clusterhat, clusterhat.com to show up. it uses the pi i2c hat logic to populate /proc/device-tree/hat

when using the raspberry pi kernel i thought it would just show up but it did not. I tried enabling i2c as described in some of the guides ive found but no change to my proc tree. do you happen to know how to fix this?

information about hat definition https://github.com/raspberrypi/hats

@mogorman I don't know much about the hat spec, but it looks like the firmware/bootloader downloads a device tree overlay from the hat. By default, NixOS uses U-Boot as a intermediate bootloader between the standard RPi bootloader and the kernel. U-Boot does not pass device tree overlays from the RPi bootloader to the kernel, which is probably why your device is not detected (this also means dtoverlay options in config.txt have no effect).

You can switch to using just the RPi bootloader w/o U-Boot, by adding boot.loader.raspberryPi.enable = true to your config, and removing boot.loader.generic-extlinux-compatible.enable = true. Note that this will cause you to lose the generation selection menu, so if you ever break your configuration, you will have to manually modify your boot partition to boot an older generation (the files are there, there is just no way to automatically boot them).

in my config i have

  # NixOS wants to enable GRUB by default
  boot.loader.grub.enable = false;
  # Enables the generation of /boot/extlinux/extlinux.conf
  boot.loader.generic-extlinux-compatible.enable = false;
  boot.loader.raspberryPi.enable = true;
  boot.loader.raspberryPi.version = 3;
  boot.loader.raspberryPi.uboot.enable = true;
  boot.kernelPackages = pkgs.linuxPackages_rpi;

but it still boots up with the generic ext linux loader every time.

@mogorman Remove this line:

boot.loader.raspberryPi.uboot.enable = true;

That option enables U-Boot, which also enables generic-extlinux-compatible behind the scenes. The difference between the the two is that raspberryPi.uboot installs the RPi U-Boot binary into the boot partition, while the generic-extlinux-compatible manages U-Boot's extlinux configuration files. generic-extlinux-compatible by itself is useful for boards that use U-Boot but have a different way of installing it that is not handled by NixOS.

@lopsided98 thank you for the advice. following that I am getting the raspberry pi firmware on boot but it doesnt seem to boot the linuxPackages_latest kernel or the rpi one when using aarch64. not sure why yet it just hangs on the rainbow screen.

I just looked at my config and remembered that I had to add:

initramfs initrd followkernel

to config.txt to get it to boot. Once you get it booted, you can that line to boot.loader.raspberryPi.firmwareConfig.

@mogorman Wait, are you using a Raspberry Pi 3? I assumed you were using a Zero because I didn't realize the clusterhat used a used a full sized Pi as well, but then I looked back at your config and saw that you had boot.loader.raspberryPi.version = 3 (of course I should have realized because you were asking about it on this PR).

In that case, your problem is probably that the RPi bootloader doesn't currently work out of the box with the RPi 3 in 64 bit mode in NixOS. By default it will look for a file named kernel8.img to boot in 64 bit mode, but NixOS installs the kernel to kernel7.img. I have a branch that fixes this, as well as another issue I forgot about with the different device tree location of the 64 bit kernel. Note that you still need the initramfs line.

@mogorman See #47250

@lopsided98 thanks will read now

Changes applied in https://git.io/fAbII.