move libcamera stuff into a separate overlay

flake.nix

@@ -37,7 +37,13 @@
   };
 
   outputs = srcs@{ self, ... }: {
-    overlay = import ./overlay (builtins.removeAttrs srcs [ "self" ]);
-    nixosModules.raspberry-pi = import ./rpi { overlay = self.overlay; };
+    overlays = {
+      core = import ./overlays (builtins.removeAttrs srcs [ "self" ]);
+      libcamera = import ./overlays/libcamera.nix (builtins.removeAttrs srcs [ "self" ]);
+    };
+    nixosModules.raspberry-pi = import ./rpi {
+      core-overlay = self.overlays.core;
+      libcamera-overlay = self.overlays.libcamera;
+    };
   };
 }

overlays/default.nix

@@ -3,9 +3,7 @@
 , rpi-firmware-src
 , rpi-firmware-nonfree-src
 , rpi-bluez-firmware-src
-, libcamera-apps-src
-, libcamera-src
-, libpisp-src
+, ...
 }:
 final: prev:
 let
@@ -40,29 +38,6 @@ in
   # the path expected by raspberry pi firmware/device tree
   compressFirmwareXz = x: x;
 
-  # A recent known working version of libcamera-apps
-  libcamera-apps =
-    final.callPackage ./libcamera-apps.nix { inherit libcamera-apps-src; };
-
-  libpisp = final.stdenv.mkDerivation {
-    name = "libpisp";
-    version = "1.0.3";
-    src = libpisp-src;
-    nativeBuildInputs = with final; [ pkg-config meson ninja ];
-    buildInputs = with final; [ nlohmann_json boost ];
-    # Meson is no longer able to pick up Boost automatically.
-    # https://github.com/NixOS/nixpkgs/issues/86131
-    BOOST_INCLUDEDIR = "${prev.lib.getDev final.boost}/include";
-    BOOST_LIBRARYDIR = "${prev.lib.getLib final.boost}/lib";
-  };
-
-  libcamera = prev.libcamera.overrideAttrs (old: {
-    version = "0.1.0";
-    src = libcamera-src;
-    buildInputs = old.buildInputs ++ (with final; [ libpisp ]);
-    patches = [ ];
-  });
-
   # provide generic rpi arm64 u-boot
   uboot_rpi_arm64 = prev.buildUBoot rec {
     defconfig = "rpi_arm64_defconfig";

overlays/libcamera.nix

@@ -0,0 +1,30 @@
+{ libcamera-apps-src
+, libcamera-src
+, libpisp-src
+, ...
+}:
+final: prev:
+{
+  # A recent known working version of libcamera-apps
+  libcamera-apps =
+    final.callPackage ./libcamera-apps.nix { inherit libcamera-apps-src; };
+
+  libpisp = final.stdenv.mkDerivation {
+    name = "libpisp";
+    version = "1.0.3";
+    src = libpisp-src;
+    nativeBuildInputs = with final; [ pkg-config meson ninja ];
+    buildInputs = with final; [ nlohmann_json boost ];
+    # Meson is no longer able to pick up Boost automatically.
+    # https://github.com/NixOS/nixpkgs/issues/86131
+    BOOST_INCLUDEDIR = "${prev.lib.getDev final.boost}/include";
+    BOOST_LIBRARYDIR = "${prev.lib.getLib final.boost}/lib";
+  };
+
+  libcamera = prev.libcamera.overrideAttrs (old: {
+    version = "0.1.0";
+    src = libcamera-src;
+    buildInputs = old.buildInputs ++ (with final; [ libpisp ]);
+    patches = [ ];
+  });
+}

rpi/default.nix

@@ -1,4 +1,4 @@
-{ overlay }:
+{ core-overlay, libcamera-overlay }:
 { lib, pkgs, config, ... }:
 
 {
@@ -12,6 +12,12 @@
           type = types.bool;
         };
       };
+      libcamera-overlay = {
+        enable = mkOption {
+          default = true;
+          type = types.bool;
+        };
+      };
     };
   };
 
@@ -171,7 +177,11 @@
       };
     };
 
-    nixpkgs = { overlays = [ overlay ]; };
+    nixpkgs = {
+      overlays = [ core-overlay ]
+        ++ (if config.raspberry-pi-nix.libcamera-overlay.enable
+      then [ libcamera-overlay ] else [ ]);
+    };
     boot = {
       initrd.availableKernelModules = [
         "usbhid"