nixos: build rpi4 sd-image

sd-image-rpi4.nix

# To build, use:
# For https://github.com/NixOS/nixpkgs/pull/68265: works (building image
# though)

# NIXPKGS_HOME=$HOME/repo/public/nixpkgs
# NIXPKGS_CONFIG=$HOME/repo/private/nixos/rpi4/sd-image-rpi4.nix
# NIX_PATH="nixpkgs=$NIXPKGS_HOME" \
#   nix-build '<nixpkgs/nixos>' -I nixos-config=$NIXPKGS_CONFIG -A config.system.build.sdImage

# For: https://github.com/NixOS/nixpkgs/pull/70796: does not work with uboot yet
# NIXPKGS_HOME=$HOME/repo/public/nixpkgs
# NIXPKGS_CONFIG=$NIXPKGS_HOME/nixos/modules/installer/cd-dvd/sd-image-raspberrypi4.nix
# NIX_PATH="nixpkgs=$NIXPKGS_HOME" \
#   nix-build '<nixpkgs/nixos>' -I nixos-config=$NIXPKGS_CONFIG -A config.system.build.sdImage

{ pkgs, ... }: {
  imports = [
    <nixpkgs/nixos/modules/installer/cd-dvd/sd-image-aarch64.nix>
  ];

  sdImage = {
    firmwareSize = 128;  # firmware partition big enough
  };

  boot = {
    kernelPackages = pkgs.linuxPackages_rpi4;
    loader = {
      raspberryPi = {
        enable = true;
        version = 4;
        uboot.enable = true;
      };
    };
  };
}