nixos/device-tree: support out-of-tree device

[qbisi]

This pr add support for thouse out-of-tree boards based on expose compileDts.

With some modification of kernel^dev, we can compile the deviceTree of a custom board without patching kernel source.
A test nixosTest.device-tree.{systemd-boot,grub} is added to valid this pr.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

---

Add a 👍 reaction to pull requests you find important.

[nix-owners]

The PR's base branch is set to staging, but 163 commits from the master branch are included. Make sure you know the right base branch for your changes, then:

• If the changes should go to the master branch, change the base branch to master
• If the changes should go to the staging branch, rebase your PR onto the merge base with the staging branch:

  # git rebase --onto $(git merge-base upstream/staging HEAD) $(git merge-base upstream/master HEAD)
  git rebase --onto 2cd2decd3aebe7bff63c51b978c27a8e91bbab3d cf62b39840dee1ff69de1cfc3561dbcc32d87f8d
  git push --force-with-lease

[qbisi]

nixpkgs-review result

Generated using nixpkgs-review.

Command: nixpkgs-review pr 403746 --package nixosTests.device-tree.systemd-boot --package nixosTests.device-tree.grub

---

aarch64-linux

✅ 2 tests built:

• nixosTests.device-tree.grub
• nixosTests.device-tree.systemd-boot

[qbisi]

cc @K900 may i have you attention on this pr.
Keeping *.dtsi file adds up 26M to linux^dev (from 779M to 805M). However the benefical is obviouse for supporting out-of-tree boards. In fact the device-tree module is making use of those dtc include header files under linux^dev.

nixpkgs/nixos/modules/hardware/device-tree.nix

Lines 92 to 108 in 88983d4

	dtboFile =
	let
	includePaths = [
	"${lib.getDev cfg.kernelPackage}/lib/modules/${cfg.kernelPackage.modDirVersion}/source/scripts/dtc/include-prefixes"
	] ++ cfg.dtboBuildExtraIncludePaths;
	extraPreprocessorFlags = cfg.dtboBuildExtraPreprocessorFlags;
	in
	if o.dtboFile == null then
	let
	dtsFile = if o.dtsFile == null then (pkgs.writeText "dts" o.dtsText) else o.dtsFile;
	in
	pkgs.deviceTree.compileDTS {
	name = "${o.name}-dtbo";
	inherit includePaths extraPreprocessorFlags dtsFile;
	}
	else
	o.dtboFile;

It's also reasonable to keep those *.dtsi file.

[jfly]

I suggest instead renaming the existing boot.loader.systemd-boot.installDeviceTree to boot.loader.efi.installDeviceTree and reusing that here (as done in the first commit of #439700).

[qbisi]

In fact, this option is more than a expilict declaration of using deviceTree command in grub.cfg.
You see i did not use the option name installDeviceTree as systemd-boot do.
There is case we put /boot in the same disk partition of /nix/store, so there's no need for grub to copy kernel/initrd/dtb to EFI partition.