config txt rendering

overlay/default.nix

@@ -74,7 +74,7 @@ in {
     fw = rpi-firmware-stable-src;
     wireless-fw = import ./raspberrypi-wireless-firmware.nix {
       bluez-firmware = rpi-bluez-firmware-src;
-      firmware-nonfree-src = rpi-firmware-nonfree-src;
+      firmware-nonfree = rpi-firmware-nonfree-src;
     };
   }] // {
     latest = final.rpi-kernels."${latest}";

overlay/raspberrypi-wireless-firmware.nix

@@ -1,14 +1,15 @@
-{ bluez-firmware-src, firmware-nonfree-src }:
+{ bluez-firmware, firmware-nonfree }:
 { lib, stdenvNoCC, fetchFromGitHub }:
 
 stdenvNoCC.mkDerivation {
   pname = "raspberrypi-wireless-firmware";
   version = "2023-01-19";
 
-  srcs = [ bluez-firmware-src firmware-nonfree-src ];
+  srcs = [ ];
 
   sourceRoot = ".";
 
+  dontUnpack = true;
   dontBuild = true;
   # Firmware blobs do not need fixing and should not be modified
   dontFixup = true;
@@ -18,14 +19,13 @@ stdenvNoCC.mkDerivation {
     mkdir -p "$out/lib/firmware/brcm"
 
     # Wifi firmware
-    cp -rv "$NIX_BUILD_TOP/firmware-nonfree/debian/config/brcm80211/." "$out/lib/firmware/"
+    cp -rv "${firmware-nonfree}/debian/config/brcm80211/." "$out/lib/firmware/"
 
     # Bluetooth firmware
-    cp -rv "$NIX_BUILD_TOP/bluez-firmware/broadcom/." "$out/lib/firmware/brcm"
+    cp -rv "${bluez-firmware}/broadcom/." "$out/lib/firmware/brcm"
 
     # CM4 symlink must be added since it's missing from upstream
     pushd $out/lib/firmware/brcm &>/dev/null
-    ln -s "./brcmfmac43455-sdio.txt" "$out/lib/firmware/brcm/brcmfmac43455-sdio.raspberrypi,4-compute-module.txt"
 
     # There are two options for the brcmfmac43455 binary: minimal or
     # standard. For more info see the readme at:

rpi/config.nix

@@ -0,0 +1,80 @@
+{ lib, config, pkgs, ... }:
+let
+  cfg = config;
+  render-raspberrypi-config = let
+    render-options = opts:
+      lib.strings.concatStringsSep "\n" (render-dt-kvs opts);
+    render-dt-param = x: "dtparam=" + x;
+    render-dt-kv = k: v:
+      if isNull v then k else let vstr = toString v; in "${k}=${vstr}";
+    render-dt-kvs = x: lib.attrsets.mapAttrsToList render-dt-kv x;
+    render-dt-overlay = { overlay, args }:
+      "dtoverlay=" + overlay + "\n"
+      + lib.strings.concatMapStringsSep "\n" render-dt-param args + "\n"
+      + "dtoverlay=";
+    render-base-dt-params = params:
+      lib.strings.concatMapStringsSep "\n" render-dt-param
+      (render-dt-kvs params);
+    render-dt-overlays = overlays:
+      lib.strings.concatMapStringsSep "\n" render-dt-overlay
+      (lib.attrsets.mapAttrsToList (k: v: {
+        overlay = k;
+        args = render-dt-kvs v;
+      }) overlays);
+    render-config-section = k:
+      { options, base-dtb-params, dt-overlays }: ''
+        [${k}]
+        ${render-options options}
+        ${render-base-dt-params base-dtb-params}
+        ${render-dt-overlays dt-overlays}
+      '';
+  in conf:
+  lib.strings.concatStringsSep "\n"
+  (lib.attrsets.mapAttrsToList render-config-section conf);
+in {
+  options = {
+    raspberrypi-config = let
+      raspberrypi-config-options = {
+        options = {
+          options = lib.mkOption {
+            type = with lib.types; attrsOf anything;
+            default = { };
+            example = {
+              enable_gic = true;
+              armstub = "armstub8-gic.bin";
+              arm_boost = true;
+            };
+          };
+          base-dtb-params = lib.mkOption {
+            type = with lib.types; attrsOf anything;
+            default = { };
+            example = {
+              i2c = "on";
+              audio = "on";
+            };
+            description = "parameters to pass to the base dtb";
+          };
+          dt-overlays = lib.mkOption {
+            type = with lib.types; attrsOf (attrsOf (nullOr str));
+            default = { };
+            example = { vc4-kms-v3d = { cma-256 = null; }; };
+            description = "dtb overlays to apply";
+          };
+        };
+      };
+    in lib.mkOption {
+      type = with lib.types; attrsOf (submodule raspberrypi-config-options);
+    };
+    raspberrypi-config-output = lib.mkOption {
+      type = lib.types.package;
+      default = pkgs.writeTextFile {
+        name = "config.txt";
+        text = ''
+          # Auto-generated by nix. Modifications will be overwritten.
+          ${render-raspberrypi-config cfg.raspberrypi-config}
+        '';
+      };
+    };
+  };
+
+}

rpi/default.nix

@@ -2,7 +2,33 @@
 { lib, pkgs, config, ... }:
 
 {
-  imports = [ ../sd-image ];
+  imports = [ ../sd-image ./config.nix ];
+
+  raspberrypi-config = {
+    pi4 = {
+      options = {
+        enable_gic = true;
+        armstub = "armstub8-gic.bin";
+        arm_boost = true;
+        disable_overscan = true;
+      };
+      dt-overlays = { vc4-kms-v3d-pi4 = { cma-512 = null; }; };
+    };
+    pi02 = { dt-overlays = { vc4-kms-v3d = { cma-256 = null; }; }; };
+    all = {
+      options = {
+        kernel = "u-boot-rpi_arm64.bin";
+        enable_uart = true;
+        avoid_warnings = true;
+        arm_64bit = true;
+      };
+      base-dtb-params = {
+        i2c = "on";
+        audio = "on";
+        krnbt = "on";
+      };
+    };
+  };
 
   nixpkgs = { overlays = [ overlay ]; };
   boot = {