nixos/systemd-boot: add support for devicetree entry

nixos/modules/system/boot/loader/systemd-boot/systemd-boot-builder.py

@@ -47,6 +47,7 @@ class BootSpec:
     toplevel: str
     specialisations: dict[str, "BootSpec"]
     sortKey: str  # noqa: N815
+    devicetree: str | None = None  # noqa: N815
     initrdSecrets: str | None = None  # noqa: N815
 
 @dataclass
@@ -84,6 +85,7 @@ class DiskEntry:
     kernel_params: str | None
     machine_id: str | None
     sort_key: str
+    devicetree: str | None
 
     @classmethod
     def from_path(cls: Type["DiskEntry"], path: Path) -> "DiskEntry":
@@ -108,7 +110,9 @@ def from_path(cls: Type["DiskEntry"], path: Path) -> "DiskEntry":
             initrd=entry_map["initrd"],
             kernel_params=entry_map.get("options"),
             machine_id=entry_map.get("machine-id"),
-            sort_key=entry_map.get("sort_key", "nixos"))
+            sort_key=entry_map.get("sort_key", "nixos"),
+            devicetree=entry_map.get("devicetree"),
+        )
         return disk_entry
 
     def write(self, sorted_first: str) -> None:
@@ -127,7 +131,8 @@ def write(self, sorted_first: str) -> None:
                 f"initrd  {self.initrd}",
                 f"options {self.kernel_params}" if self.kernel_params is not None else None,
                 f"machine-id {self.machine_id}" if self.machine_id is not None else None,
-                f"sort-key {default_sort_key if self.default else self.sort_key}"
+                f"sort-key {default_sort_key if self.default else self.sort_key}",
+                f"devicetree {self.devicetree}" if self.devicetree is not None else None,
             ]
 
             f.write("\n".join(filter(None, boot_entry)))
@@ -233,10 +238,12 @@ def bootspec_from_json(bootspec_json: dict[str, Any]) -> BootSpec:
     specialisations = {k: bootspec_from_json(v) for k, v in specialisations.items()}
     systemdBootExtension = bootspec_json.get('org.nixos.systemd-boot', {})
     sortKey = systemdBootExtension.get('sortKey', 'nixos')
+    devicetree = systemdBootExtension.get('devicetree')
     return BootSpec(
         **bootspec_json['org.nixos.bootspec.v1'],
         specialisations=specialisations,
-        sortKey=sortKey
+        sortKey=sortKey,
+        devicetree=devicetree,
     )
 
 
@@ -261,6 +268,7 @@ def write_entry(profile: str | None,
         bootspec = bootspec.specialisations[specialisation]
     kernel = copy_from_file(bootspec.kernel)
     initrd = copy_from_file(bootspec.initrd)
+    devicetree = copy_from_file(bootspec.devicetree) if bootspec.devicetree is not None else None
 
     title = "{name}{profile}{specialisation}".format(
         name=DISTRO_NAME,
@@ -303,6 +311,7 @@ def write_entry(profile: str | None,
         machine_id=machine_id,
         description=f"Generation {generation} {bootspec.label}, built on {build_date}",
         sort_key=bootspec.sortKey,
+        devicetree=devicetree,
         default=current
     ).write(sorted_first)
 

nixos/modules/system/boot/loader/systemd-boot/systemd-boot.nix

@@ -191,6 +191,15 @@ in {
       '';
     };
 
+    installDeviceTree = mkOption {
+      default = with config.hardware.deviceTree; enable && name != null;
+      defaultText = ''with config.hardware.deviceTree; enable && name != null'';
+      description = ''
+        Install the devicetree blob specified by `config.hardware.deviceTree.name`
+        to the ESP and instruct systemd-boot to pass this DTB to linux.
+      '';
+    };
+
     extraInstallCommands = mkOption {
       default = "";
       example = ''
@@ -353,6 +362,10 @@ in {
         assertion = (config.boot.kernelPackages.kernel.features or { efiBootStub = true; }) ? efiBootStub;
         message = "This kernel does not support the EFI boot stub";
       }
+      {
+        assertion = cfg.installDeviceTree -> config.hardware.deviceTree.enable -> config.hardware.deviceTree.name != null;
+        message = "Cannot install devicetree without 'config.hardware.deviceTree.enable' enabled and 'config.hardware.deviceTree.name' set";
+      }
     ] ++ concatMap (filename: [
       {
         assertion = !(hasInfix "/" filename);
@@ -410,6 +423,7 @@ in {
 
     boot.bootspec.extensions."org.nixos.systemd-boot" = {
       inherit (config.boot.loader.systemd-boot) sortKey;
+      devicetree = lib.mkIf cfg.installDeviceTree "${config.hardware.deviceTree.package}/${config.hardware.deviceTree.name}";
     };
 
     system = {

nixos/tests/systemd-boot.nix

@@ -172,10 +172,23 @@ rec {
       imports = [ common ];
       specialisation.something.configuration = {
         boot.loader.systemd-boot.sortKey = "something";
+
+        # Since qemu will dynamically create a devicetree blob when starting
+        # up, it is not straight forward to create an export of that devicetree
+        # blob without knowing before-hand all the flags we would pass to qemu
+        # (we would then be able to use `dumpdtb`). Thus, the following config
+        # will not boot, but it does allow us to assert that the boot entry has
+        # the correct contents.
+        boot.loader.systemd-boot.installDeviceTree = pkgs.stdenv.hostPlatform.isAarch64;
+        hardware.deviceTree.name = "dummy.dtb";
+        hardware.deviceTree.package = lib.mkForce (pkgs.runCommand "dummy-devicetree-package" { } ''
+          mkdir -p $out
+          cp ${pkgs.emptyFile} $out/dummy.dtb
+        '');
       };
     };
 
-    testScript = ''
+    testScript = { nodes, ... }: ''
       machine.start()
       machine.wait_for_unit("multi-user.target")
 
@@ -188,6 +201,10 @@ rec {
       machine.succeed(
           "grep 'sort-key something' /boot/loader/entries/nixos-generation-1-specialisation-something.conf"
       )
+    '' + pkgs.lib.optionalString pkgs.stdenv.hostPlatform.isAarch64 ''
+      machine.succeed(
+          "grep 'devicetree .*dummy' /boot/loader/entries/nixos-generation-1-specialisation-something.conf"
+      )
     '';
   };