nixos-hardware/raspberry-pi/4/apply-overlays-dtmerge.nix

# modification of nixpkgs deviceTree.applyOverlays to resolve https://github.com/NixOS/nixpkgs/issues/125354
# https://github.com/NixOS/nixpkgs/blob/master/pkgs/os-specific/linux/device-tree/default.nix
{ lib, pkgs, stdenvNoCC, dtc, libraspberrypi }:

with lib; (base: overlays': stdenvNoCC.mkDerivation {
  name = "device-tree-overlays";
  nativeBuildInputs = [ dtc libraspberrypi ];
  buildCommand = let
    overlays = toList overlays';
  in ''
    mkdir -p $out
    cd ${base}
    find . -type f -name '*.dtb' -print0 \
      | xargs -0 cp -v --no-preserve=mode --target-directory $out --parents
    for dtb in $(find $out -type f -name '*.dtb'); do
      dtbCompat="$( fdtget -t s $dtb / compatible )"
      ${flip (concatMapStringsSep "\n") overlays (o: ''
      overlayCompat="$( fdtget -t s ${o.dtboFile} / compatible )"
      # overlayCompat in dtbCompat
      if [[ "$dtbCompat" =~ "$overlayCompat" ]]; then
        echo "Applying overlay ${o.name} to $( basename $dtb )"
        mv $dtb{,.in}
        cp ${o.dtboFile}{,.dtbo}
        dtmerge "$dtb.in" "$dtb" ${o.dtboFile}.dtbo;
        rm $dtb.in ${o.dtboFile}.dtbo
      fi
      '')}
    done
  '';
})