update default rpi config

README.md

@@ -1,27 +1,22 @@
 # raspberry-pi-nix
 
-NixOS modules that make building images for raspberry-pi products
-easier. Most of the work in this repository is based on work in
-[nixos-hardware](https://github.com/NixOS/nixos-hardware) and
-[nixpkgs](https://github.com/NixOS/nixpkgs). Additionally, be aware
-that I am no expert and this repo is the product of me fooling around
-with some pis.
+The primary goal of this software is to make it easy to create
+working NixOS configurations for Raspberry Pi products. Specifically,
+this repository aims to deliver the following benefits:
 
-This flake provides nixos modules that correspond to different
-raspberry-pi products. These modules can be included in nixos
-configurations and aim to deliver the following benefits:
-
-1. Configure the kernel, device tree, and u-boot in a way that is
-   compatible with the hardware.
-2. Provide a nix interface to device tree configuration that will be
-   familiar to those who have used raspberry-pi's config.txt based
-   configuration.
+1. Configure the kernel, device tree, and boot loader in a way that is
+   compatible with the hardware and proprietary firmware.
+2. Provide a nix interface to Raspberry Pi/device tree configuration
+   that will be familiar to those who have used Raspberry Pi's
+   [config.txt based
+   configuration](https://www.raspberrypi.com/documentation/computers/config_txt.html).
 3. Make it easy to build an image suitable for flashing to an sd-card,
    without a need to first go through an installation media.
-   
+
 The important modules are `overlay/default.nix`, `rpi/default.nix`,
-and `rpi/device-tree.nix`. The other modules for i2c, i2s, etc are
-mostly wrappers that set common device tree settings for you.
+and `rpi/config.nix`. The other modules for i2c, i2s, etc are mostly
+wrappers that set `config.txt` settings and enable required kernel
+modules.
 
 ## Example
 
@@ -46,27 +41,12 @@ mostly wrappers that set common device tree settings for you.
           useDHCP = false;
           interfaces = { wlan0.useDHCP = true; };
         };
-        hardware.raspberry-pi = {
-          i2c.enable = true;
-          audio.enable = true;
-          fkms-3d.enable = true;
-          deviceTree = {
-            dt-overlays = [{
-              overlay = "imx477"; # add the overlay for the HQ camera
-              args = [ ];
-            }];
-          };
-        };
       };
     in {
       nixosConfigurations = {
-        rpi-zero-2-w-example = nixosSystem {
+        rpi-example = nixosSystem {
           system = "aarch64-linux";
-          modules = [ raspberry-pi-nix.rpi-zero-2-w basic-config ];
-        };
-        rpi-4b-example = nixosSystem {
-          system = "aarch64-linux";
-          modules = [ raspberry-pi-nix.rpi-4b basic-config ];
+          modules = [ raspberry-pi-nix.rpi basic-config ];
         };
       };
     };
@@ -77,25 +57,64 @@ mostly wrappers that set common device tree settings for you.
 
 An image suitable for flashing to an sd-card can be found at the
 attribute `config.system.build.sdImage`. For example, if you wanted to
-build an image for `rpi-zero-2-w-example` in the above configuration
+build an image for `rpi-example` in the above configuration
 example you could run:
 
 ```
-nix build '.#nixosConfigurations.rpi-zero-2-w-example.config.system.build.sdImage'
+nix build '.#nixosConfigurations.rpi-example.config.system.build.sdImage'
 ```
 
-## Other notes
+## The firmware partition
 
-The sd-image built is partitioned in the same way as the aarch64
-installation media from nixpkgs: There is a firmware partition that
-contains necessary firmware, u-boot, and config.txt. Then there is
-another partition that contains everything else. After the sd-image is
-built, nixos system updates will not change anything in the firmware
-partition ever again. New kernels and device tree configurations will
-remain on the nixos partition and be booted by u-boot in the firmware
+The image produced by this package is partitioned in the same way as
+the aarch64 installation media from nixpkgs: There is a firmware
+partition that contains necessary firmware, u-boot, and
+config.txt. Then there is another partition (labeled `NIXOS_SD`) that
+contains everything else. The firmware and `config.txt` file are
+managed by NixOS modules defined in this package. Additionally, NixOS
+system activation will update the firmware and `config.txt` in the
+firmware partition __in place__. Linux kernels are stored in the
+`NIXOS_SD` partition and will be booted by u-boot in the firmware
 partition.
 
-So, while you can control device tree params and overlays through your
-nixos system configuration, if you want to modify other config.txt
-variables this must be done manually by mounting the partition and
-modifying the config.txt file.
+## `config.txt` generation
+
+As noted, the `config.txt` file is generated by the NixOS
+configuration and automatically updated on system activation. 
+
+
+## Firmware partition implementation notes
+
+In Raspberry Pi devices the proprietary firmware manipulates the
+device tree in a number of ways before handing it off to the kernel
+(or in our case, to u-boot). The transformations that are performed
+aren't documented so well (although I have found [this
+list](https://forums.raspberrypi.com/viewtopic.php?t=329799#p1974233)
+). 
+
+This manipulation makes it difficult to use the device tree configured
+directly by NixOS as you must know and reproduce the manipulation
+performed by the proprietary firmware.
+
+Even if the manipulation was reproduced, some convenience would be
+missed out. For example, the firmware can detect hardware during boot
+and automatically configure the device tree accordingly, rather than
+requiring a NixOS system rebuild with a different device tree for
+different hardware. Examples of what I mean by hardware include: the
+specific Raspberry Pi device booting the image, connected cameras, and
+connected displays.
+
+So, in order to avoid the headaches associated with failing to
+reproduce some firmware device tree manipulation, and to reap the
+benefits afforded by the firmware device tree configuration, u-boot is
+configured to use the device tree that it is given (i.e. the one that
+the raspberry pi firmware loads and manipulates). As a consequence,
+device tree configuration is controlled via the [config.txt
+file](https://www.raspberrypi.com/documentation/computers/config_txt.html).
+
+Additionally, the firmware, device trees, and overlays from the
+`raspberrypifw` package populates the firmware partition on system
+activation. This package is kept up to date by the overlay applied by
+this package, so you don't need configure this. However, if you want
+to use different firmware you can override that package to do so.
+

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;
+    };
+  };
+}

sd-image/default.nix

@@ -16,7 +16,7 @@
       populateFirmwareCommands = ''
         cp ${pkgs.uboot_rpi_arm64}/u-boot.bin firmware/u-boot-rpi-arm64.bin
         cp -r ${pkgs.raspberrypifw}/share/raspberrypi/boot/{start*.elf,*.dtb,bootcode.bin,fixup*.dat,overlays} firmware
-        cp ${config.raspberrypi-config-output} firmware/config.txt
+        cp ${config.hardware.raspberry-pi.config-output} firmware/config.txt
       '';
       populateRootCommands = ''
         mkdir -p ./files/boot

sd-image/sd-image.nix

@@ -162,6 +162,7 @@ in {
       "/boot/firmware" = {
         device = "/dev/disk/by-label/${config.sdImage.firmwarePartitionName}";
         fsType = "vfat";
+        options = [ "nofail" "noauto" ];
       };
       "/" = {
         device = "/dev/disk/by-label/NIXOS_SD";