nixops: work around devicetree breakage in nixpkgs

This reverts the effects of nixpkgs commit 6c9df40a4bc819fcab0836ad28ee944c8ce66db0
and restores the old behavior.

nixops/device-tree-module.nix

@@ -0,0 +1,67 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.hardware.deviceTree;
+in {
+  options = {
+      hardware.deviceTree = {
+        enable = mkOption {
+          default = pkgs.stdenv.hostPlatform.platform.kernelDTB or false;
+          type = types.bool;
+          description = ''
+            Build device tree files. These are used to describe the
+            non-discoverable hardware of a system.
+          '';
+        };
+
+        base = mkOption {
+          default = "${config.boot.kernelPackages.kernel}/dtbs";
+          defaultText = "\${config.boot.kernelPackages.kernel}/dtbs";
+          example = literalExample "pkgs.device-tree_rpi";
+          type = types.path;
+          description = ''
+            The path containing the base device-tree (.dtb) to boot. Contains
+            device trees bundled with the Linux kernel by default.
+          '';
+        };
+
+        name = mkOption {
+          default = null;
+          example = "some-dtb.dtb";
+          type = types.nullOr types.str;
+          description = ''
+            The name of an explicit dtb to be loaded, relative to the dtb base.
+            Useful in extlinux scenarios if the bootloader doesn't pick the
+            right .dtb file from FDTDIR.
+          '';
+        };
+
+        overlays = mkOption {
+          default = [];
+          example = literalExample
+            "[\"\${pkgs.device-tree_rpi.overlays}/w1-gpio.dtbo\"]";
+          type = types.listOf types.path;
+          description = ''
+            A path containing device tree overlays (.dtbo) to be applied to all
+            base device-trees.
+          '';
+        };
+
+        package = mkOption {
+          default = null;
+          type = types.nullOr types.path;
+          internal = true;
+          description = ''
+            A path containing the result of applying `overlays` to `base`.
+          '';
+        };
+      };
+  };
+
+  config = mkIf (cfg.enable) {
+    hardware.deviceTree.package = if (cfg.overlays != [])
+      then pkgs.deviceTree.applyOverlays cfg.base cfg.overlays else cfg.base;
+  };
+}

nixops/device-tree-pkg.nix

@@ -0,0 +1,17 @@
+{ stdenvNoCC, dtc, findutils }:
+
+with stdenvNoCC.lib; {
+  applyOverlays = (base: overlays: stdenvNoCC.mkDerivation {
+    name = "device-tree-overlays";
+    nativeBuildInputs = [ dtc findutils ];
+    buildCommand = let
+      quotedDtbos = concatMapStringsSep " " (o: "\"${toString o}\"") (toList overlays);
+    in ''
+      for dtb in $(find ${base} -name "*.dtb" ); do
+        outDtb=$out/$(realpath --relative-to "${base}" "$dtb")
+        mkdir -p "$(dirname "$outDtb")"
+        fdtoverlay -o "$outDtb" -i "$dtb" ${quotedDtbos};
+      done
+    '';
+  });
+}

nixops/rpi-server.nix

@@ -20,9 +20,17 @@
   boot.kernelParams = ["cma=64M"]; # work around https://github.com/raspberrypi/linux/issues/3208
   boot.kernelPackages = if rpi4 then pkgs.linuxPackages_rpi4 else pkgs.linuxPackages_rpi3;
   boot.initrd.includeDefaultModules = false;
+
+  # work around https://github.com/NixOS/nixpkgs/issues/125354
+  disabledModules = [ "hardware/device-tree.nix" ];
+  imports = [ ./device-tree-module.nix ];
+  nixpkgs.config.packageOverrides = super: let self = super.pkgs; in {
+    deviceTree = super.callPackage ./device-tree-pkg.nix {};
+  };
   hardware.deviceTree.enable = true;
-  hardware.deviceTree.filter = "*rpi*.dtb";
-  hardware.deviceTree.overlays = [ { name = "poe"; dtboFile = "${pkgs.device-tree_rpi.overlays}/rpi-poe.dtbo"; } ];
+  hardware.deviceTree.base = pkgs.device-tree_rpi;
+  hardware.deviceTree.overlays = [ "${pkgs.device-tree_rpi.overlays}/rpi-poe.dtbo" ];
+
 
   fileSystems = {
     "/" = {

nixops/rpi.nix

@@ -16,9 +16,17 @@ in
   boot.kernelParams = if rpi4 then ["cma=64M"] else []; # work around https://github.com/raspberrypi/linux/issues/3208
   boot.kernelPackages = if rpi4 then pkgs.linuxPackages_rpi4 else pkgs.linuxPackages_rpi3;
   boot.initrd.includeDefaultModules = false;
+
+  # work around https://github.com/NixOS/nixpkgs/issues/125354
+  disabledModules = [ "hardware/device-tree.nix" ];
+  imports = [ ./device-tree-module.nix ];
+  nixpkgs.config.packageOverrides = super: let self = super.pkgs; in {
+    deviceTree = super.callPackage ./device-tree-pkg.nix {};
+  };
   hardware.deviceTree.enable = true;
-  hardware.deviceTree.filter = "*rpi*.dtb";
-  hardware.deviceTree.overlays = [ { name = "poe"; dtboFile = "${pkgs.device-tree_rpi.overlays}/rpi-poe.dtbo"; } ];
+  hardware.deviceTree.base = pkgs.device-tree_rpi;
+  hardware.deviceTree.overlays = [ "${pkgs.device-tree_rpi.overlays}/rpi-poe.dtbo" ];
+
 
   fileSystems = {
     "/" = {