update default rpi config

rpi/config.nix

@@ -1,6 +1,6 @@
 { lib, config, pkgs, ... }:
 let
-  cfg = config;
+  cfg = config.hardware.raspberry-pi;
   render-raspberrypi-config = let
     render-options = opts:
       lib.strings.concatStringsSep "\n" (render-dt-kvs opts);
@@ -22,11 +22,11 @@ let
         args = render-dt-kvs v;
       }) overlays);
     render-config-section = k:
-      { options, base-dtb-params, dt-overlays }:
+      { options, base-dt-params, dt-overlays }:
       let
         all-config = lib.concatStringsSep "\n" (lib.filter (x: x != "") [
           (render-options options)
-          (render-base-dt-params base-dtb-params)
+          (render-base-dt-params base-dt-params)
           (render-dt-overlays dt-overlays)
         ]);
       in ''
@@ -38,48 +38,48 @@ let
   (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;
+    hardware.raspberry-pi = {
+      config = let
+        raspberry-pi-config-options = {
+          options = {
+            options = lib.mkOption {
+              type = with lib.types; attrsOf anything;
+              default = { };
+              example = {
+                enable_gic = true;
+                arm_boost = true;
+              };
             };
-          };
-          base-dtb-params = lib.mkOption {
-            type = with lib.types; attrsOf anything;
-            default = { };
-            example = {
-              i2c = "on";
-              audio = "on";
+            base-dt-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";
             };
-            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 raspberry-pi-config-options);
       };
-    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}
-        '';
+      config-output = lib.mkOption {
+        type = lib.types.package;
+        default = pkgs.writeTextFile {
+          name = "config.txt";
+          text = ''
+            # This is a generated file. Do not edit!
+            ${render-raspberrypi-config cfg.config}
+          '';
+        };
       };
     };
   };
-
 }

rpi/default.nix

@@ -2,8 +2,10 @@
 { lib, pkgs, config, ... }:
 
 {
-  imports = [ ../sd-image ./config.nix ];
+  imports = [ ../sd-image ./config.nix ./i2c.nix ];
 
+  # On activation install u-boot, Raspberry Pi firmware, and our
+  # generated config.txt
   system.activationScripts.raspberrypi = {
     text = ''
       if ! grep -qs '/boot/firmware ' /proc/mounts; then
@@ -11,29 +13,28 @@
       fi
       cp ${pkgs.uboot_rpi_arm64}/u-boot.bin /boot/firmware/u-boot-rpi-arm64.bin
       cp -r ${pkgs.raspberrypifw}/share/raspberrypi/boot/{start*.elf,*.dtb,bootcode.bin,fixup*.dat,overlays} /boot/firmware
-      cp ${config.raspberrypi-config-output} /boot/firmware/config.txt
+      cp ${config.hardware.raspberry-pi.config-output} /boot/firmware/config.txt
     '';
   };
 
-  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; }; }; };
+  # Default config.txt on Raspberry Pi OS:
+  # https://github.com/RPi-Distro/pi-gen/blob/master/stage1/00-boot-files/files/config.txt
+  hardware.raspberry-pi.config = {
+    cm4 = { options = { otg_mode = true; }; };
+    pi4 = { options = { arm_boost = true; }; };
     all = {
       options = {
+        # The firmware will start our u-boot binary rather than a
+        # linux kernel.
         kernel = "u-boot-rpi-arm64.bin";
+        arm_64bit = true;
         enable_uart = true;
         avoid_warnings = true;
-        arm_64bit = true;
+        camera_auto_detect = true;
+        display_auto_detect = true;
+        disable_overscan = true;
       };
-      base-dtb-params = { krnbt = "on"; };
+      dt-overlays = { vc4-kms-v3d = { }; };
     };
   };
 
@@ -59,4 +60,12 @@
     };
   };
   hardware.enableRedistributableFirmware = true;
+
+  services = {
+    udev.extraRules = ''
+      SUBSYSTEM=="dma_heap", GROUP="video", MODE="0660"
+      KERNEL=="gpiomem", GROUP="gpio", MODE="0660"
+      KERNEL=="gpiochip*", GROUP="gpio", MODE="0660"
+    '';
+  };
 }

rpi/i2c.nix

@@ -0,0 +1,14 @@
+{ config, lib, pkgs, ... }:
+
+let cfg = config.hardware.raspberry-pi.i2c;
+in {
+  options.hardware.raspberry-pi.i2c = {
+    enable = lib.mkEnableOption "configuration for i2c";
+  };
+  config = lib.mkIf cfg.enable {
+    hardware = {
+      raspberry-pi.config.all.base-dt-params = { i2c = "on"; };
+      i2c.enable = true;
+    };
+  };
+}