From 672368db8343fc43a2b408febca3ac5821ffb607 Mon Sep 17 00:00:00 2001
From: Yingchi Long <i@lyc.dev>
Date: Sat, 4 May 2024 10:48:22 +0800
Subject: [PATCH] nixos/aplaz: use `x86_64-linux` metis for crossing compiling
 the kernel

---
 nixos/configurations/aplaz/cross.nix   | 28 ++++++++++++++++++++++++++
 nixos/configurations/aplaz/default.nix |  1 +
 nixos/modules/nix.nix                  |  1 +
 3 files changed, 30 insertions(+)
 create mode 100644 nixos/configurations/aplaz/cross.nix

diff --git a/nixos/configurations/aplaz/cross.nix b/nixos/configurations/aplaz/cross.nix
new file mode 100644
index 00000000..58335c39
--- /dev/null
+++ b/nixos/configurations/aplaz/cross.nix
@@ -0,0 +1,28 @@
+# Specify cross-builds on aplaz.
+{ pkgs, inputs, lib, config, ... }:
+let
+  pkgsX86Cross = import pkgs.path {
+    crossSystem.system = "aarch64-linux";
+    localSystem.system = "x86_64-linux";
+    overlays = [ inputs.nixos-apple-silicon.overlays.apple-silicon-overlay ];
+  };
+in
+{
+  nix.buildMachines = [
+    {
+      hostName = "metis";
+      system = "x86_64-linux";
+      protocol = "ssh";
+      supportedFeatures = [ "nixos-test" "benchmark" "big-parallel" "kvm" ];
+      mandatoryFeatures = [ ];
+    }
+  ];
+
+  nix.distributedBuilds = true;
+
+  # Use x86_64 linux cross-compiled kernel.
+  boot.kernelPackages = lib.mkForce (pkgsX86Cross.linux-asahi.override {
+    _kernelPatches = config.boot.kernelPatches;
+    withRust = config.hardware.asahi.withRust;
+  });
+}
diff --git a/nixos/configurations/aplaz/default.nix b/nixos/configurations/aplaz/default.nix
index 7f47c907..f83decdd 100644
--- a/nixos/configurations/aplaz/default.nix
+++ b/nixos/configurations/aplaz/default.nix
@@ -10,6 +10,7 @@ in
 {
   imports = [
     # Include the results of the hardware scan.
+    ./cross.nix
     ./hardware-configuration.nix
     ./wireguard.nix
     inputs.nixos-apple-silicon.nixosModules.apple-silicon-support
diff --git a/nixos/modules/nix.nix b/nixos/modules/nix.nix
index d4592be0..49d7c631 100644
--- a/nixos/modules/nix.nix
+++ b/nixos/modules/nix.nix
@@ -23,6 +23,7 @@
       warn-dirty = false;
       system-features = [ "kvm" "big-parallel" ];
       use-xdg-base-directories = true;
+      builders-use-substitutes = true;
     };
     package = pkgs.nixUnstable;
     gc = {