raspberry-pi/common: add firmware-partition install module
Adds hardware.raspberry-pi.firmware to stage the Pi's pre-Linux boot files (GPU boot code, DTBs, overlays, config.txt, optionally U-Boot) onto the firmware partition. Boards still boot via generic-extlinux-compatible; this only supplies the files it needs, through populateCmd for image builders or an opt-in activation script. DTB/overlay copy adapted from nvmd/nixos-raspberrypi.
This commit is contained in:
Jamie Magee
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3 changed files with 230 additions and 4 deletions
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@ -4,7 +4,7 @@ NixOS profiles and modules for Raspberry Pi boards.
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## What's here
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- `common/` has the shared bits: the `linux-rpi` kernel build (vendor defconfig, matching firmware), the `config.txt` generation module, and a pinned wireless firmware.
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- `common/` has the shared bits: the `linux-rpi` kernel build (vendor defconfig, matching firmware), the `config.txt` generation module, a pinned wireless firmware, and the firmware-partition install module.
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- `2/`, `3/`, `4/`, `5/` are the board profiles. Each one picks the right kernel and kernel params. Pi 4 and 5 also set DT filters and the initrd modules they need.
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- The extra files under `4/` are opt-in toggles for Pi 4 hardware: audio, dwc2, GPIO, I2C, LEDs, the PoE HATs, touchscreens, and so on.
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@ -18,7 +18,28 @@ NixOS profiles and modules for Raspberry Pi boards.
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}
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```
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These profiles assume the `generic-extlinux-compatible` bootloader (the NixOS module that writes an `extlinux.conf` for U-Boot to read), which is what aarch64 NixOS SD images use by default. There is no `boot.loader.raspberry-pi` module here. U-Boot itself still has to land on the boot partition somehow. Either your image builder does it, or you do. Nothing in here writes to `/boot/firmware/`. See [Current limits](#current-limits).
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These profiles assume the `generic-extlinux-compatible` bootloader (the NixOS module that writes an `extlinux.conf` for U-Boot to read), which is what aarch64 NixOS SD images use by default. There is no `boot.loader.raspberry-pi` module here. U-Boot and the GPU boot code still have to land on the firmware partition somehow: either your image builder does it, or you use the firmware install module below.
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## Firmware install
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`hardware.raspberry-pi.firmware` stages the files the Pi firmware needs before Linux starts onto the firmware partition (default `/boot/firmware`): GPU boot code (`bootcode.bin`, `start*.elf`, `fixup*.dat`), vendor device trees and overlays, the rendered `config.txt`, and optionally U-Boot. It is not a new boot method; it just supplies the files the existing `generic-extlinux-compatible` + U-Boot path needs.
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When you build an SD image, the module sets `sdImage.populateFirmwareCommands` itself, so the firmware partition is populated at build time with no extra configuration.
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For a running system, set `hardware.raspberry-pi.firmware.enable = true`. An activation script then repopulates the firmware partition on every `nixos-rebuild switch`. It is off by default.
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To chainload U-Boot from the firmware, enable `uboot.enable`. It copies `u-boot.bin` to the firmware partition and sets `config.txt`'s `kernel` line for you:
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```nix
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{
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hardware.raspberry-pi.firmware = {
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enable = true;
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uboot.enable = true;
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};
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}
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```
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`uboot.enable` defaults `uboot.package` to nixpkgs' `pkgs.ubootRaspberryPiAarch64`, built from the upstream `rpi_arm64_defconfig`, which covers every 64-bit board (Pi 3/4/5). For a 32-bit board, override `uboot.package` with the matching U-Boot build. On the Pi 5 this boots from SD, but U-Boot can't drive USB/PCIe/RP1 yet, so USB boot, NVMe boot, and a USB keyboard at the U-Boot prompt don't work until Linux takes over.
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## `config.txt`
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@ -51,6 +72,6 @@ Top-level attrs are conditional sections (`all`, `pi4`, `pi5`, `cm4`, and so on)
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## Current limits
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- No firmware install: Nothing writes `start*.elf`, `bootcode.bin`, `fixup*.dat`, vendor DTBs, overlays, or `config.txt` to `/boot/firmware/`. The rendered config.txt is exposed at `hardware.raspberry-pi.configtxt.file`, but nothing on disk reads it yet. You either rely on the SD-image populate step or stage those files yourself.
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- No bootloader module: There's no `boot.loader.raspberry-pi` here. Boards rely on `generic-extlinux-compatible` plus U-Boot. Pi 5 boots from SD via U-Boot, but USB, PCIe, and the RP1 don't come up until Linux takes over. So a USB keyboard at the U-Boot prompt won't work on Pi 5 today.
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- No bootloader module: There's no `boot.loader.raspberry-pi` here. Boards rely on `generic-extlinux-compatible` plus U-Boot. Raspberry Pi OS has the GPU firmware load the kernel directly; we go through U-Boot so it reads `extlinux.conf`, which is what gives you the NixOS boot-generation menu and rollbacks. The firmware install module just stages the boot code and (optionally) U-Boot; it doesn't add a firmware-level direct-boot path. Pi 5 boots from SD via U-Boot, but USB, PCIe, and the RP1 don't come up until Linux takes over, so a USB keyboard at the U-Boot prompt won't work on Pi 5 today.
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- Single pinned kernel: `common/kernel.nix` pins one `linux-rpi` version rather than matching each kernel to its firmware release.
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- No Pi 0/02/1 board profiles: `common/kernel.nix` accepts `rpiVersion = 1`, but there's no `0/`, `02/`, or `1/` directory wiring that kernel up into a profile you can import via `<nixos-hardware/raspberry-pi/...>`.
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@ -2,6 +2,7 @@
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imports = [
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./config-txt.nix
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./config-txt-defaults.nix
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./firmware.nix
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];
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boot.initrd.availableKernelModules = [
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204
raspberry-pi/common/firmware.nix
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204
raspberry-pi/common/firmware.nix
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@ -0,0 +1,204 @@
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# Firmware-partition install for Raspberry Pi.
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#
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# Stages the files the Pi needs before Linux starts onto the firmware partition
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# (default /boot/firmware): GPU boot code (bootcode.bin, start*.elf, fixup*.dat),
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# vendor device trees and overlays, the rendered config.txt, and optionally
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# U-Boot. Not a new boot method: boards still use
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# boot.loader.generic-extlinux-compatible (U-Boot reads extlinux.conf); this just
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# provides the files that path needs, either at SD-image build time
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# (sdImage.populateFirmwareCommands, wired automatically) or on a running system
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# (the opt-in activation script).
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#
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# DTB/overlay copy adapted from nvmd/nixos-raspberrypi (MIT).
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{
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lib,
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config,
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options,
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pkgs,
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...
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}:
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let
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cfg = config.hardware.raspberry-pi.firmware;
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# install-rpi-firmware <target-dir>
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# Idempotent: copies via temp file + rename, and prunes stale DTBs/overlays.
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installScript = pkgs.writeShellApplication {
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name = "install-rpi-firmware";
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runtimeInputs = [ pkgs.coreutils ];
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text = ''
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target="$1"
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shopt -s nullglob
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firmwareBoot=${cfg.package}/share/raspberrypi/boot
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${
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if cfg.useGenerationDeviceTree then
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''
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# Prefer the booted generation's device trees over the vendor ones.
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dtbSrc=/run/current-system/dtbs
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[ -d "$dtbSrc" ] || dtbSrc=$firmwareBoot
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''
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else
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''
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dtbSrc=$firmwareBoot
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''
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}
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mkdir -p "$target/overlays"
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# Copy via a temp file then rename so an interrupted run can't leave a
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# half-written file behind. The firmware partition is FAT, so the rename
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# isn't truly atomic, but it still beats a partial copy when the
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# activation script rewrites the partition on a live system.
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copyForced() {
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cp "$1" "$2.tmp"
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mv "$2.tmp" "$2"
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}
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# Track every file we copy this run, keyed by destination path, so the
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# prune step below can delete stale device trees / overlays left behind
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# by a previous generation.
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declare -A kept
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echo "rpi-firmware: copying device trees from $dtbSrc"
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for dtb in "$dtbSrc"/*.dtb "$dtbSrc"/broadcom/*.dtb; do
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dst="$target/$(basename "$dtb")"
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copyForced "$dtb" "$dst"
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kept[$dst]=1
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done
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if [ -d "$dtbSrc/overlays" ]; then
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for ovr in "$dtbSrc"/overlays/*; do
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dst="$target/overlays/$(basename "$ovr")"
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copyForced "$ovr" "$dst"
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kept[$dst]=1
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done
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fi
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# Prune stale device trees / overlays.
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for fn in "$target"/*.dtb "$target"/overlays/*; do
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if [ "''${kept[$fn]:-}" != 1 ]; then
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rm -v -- "$fn"
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fi
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done
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echo "rpi-firmware: copying GPU boot code"
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for src in "$firmwareBoot"/bootcode.bin "$firmwareBoot"/start*.elf "$firmwareBoot"/fixup*.dat; do
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copyForced "$src" "$target/$(basename "$src")"
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done
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${lib.optionalString cfg.uboot.enable ''
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echo "rpi-firmware: copying U-Boot"
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copyForced ${cfg.uboot.package}/u-boot.bin "$target/u-boot.bin"
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''}
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echo "rpi-firmware: copying config.txt"
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copyForced ${config.hardware.raspberry-pi.configtxt.file} "$target/config.txt"
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echo "rpi-firmware: done ($target)"
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'';
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};
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in
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{
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options.hardware.raspberry-pi.firmware = {
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enable = lib.mkEnableOption ''
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installation of the Raspberry Pi firmware partition on a running system.
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An activation script repopulates {option}`hardware.raspberry-pi.firmware.path`
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on every system switch
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'';
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path = lib.mkOption {
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type = lib.types.str;
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default = "/boot/firmware";
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description = ''
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Mount point of the Raspberry Pi firmware (FAT) partition.
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`/boot/firmware` matches the NixOS aarch64 SD-image layout, and most
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configurations should leave it there. The activation script writes here
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only when it is a mounted partition (checked with `mountpoint`);
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otherwise it logs a warning and skips.
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'';
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};
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package = lib.mkOption {
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type = lib.types.package;
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default = pkgs.raspberrypifw;
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defaultText = lib.literalExpression "pkgs.raspberrypifw";
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description = ''
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Package providing the Raspberry Pi GPU boot code, vendor device trees,
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and overlays under `''${package}/share/raspberrypi/boot`.
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'';
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};
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uboot = {
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enable = lib.mkEnableOption ''
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chainloading U-Boot from the Raspberry Pi firmware.
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Copies `u-boot.bin` from
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{option}`hardware.raspberry-pi.firmware.uboot.package` to the firmware
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partition and points `config.txt`'s `kernel` at it, so the GPU firmware
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loads U-Boot, which then reads `extlinux.conf`
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'';
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package = lib.mkOption {
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type = lib.types.package;
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default = pkgs.ubootRaspberryPiAarch64;
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defaultText = lib.literalExpression "pkgs.ubootRaspberryPiAarch64";
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description = ''
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U-Boot package whose `u-boot.bin` is copied to the firmware
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partition when {option}`hardware.raspberry-pi.firmware.uboot.enable`
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is enabled.
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The default, nixpkgs' `pkgs.ubootRaspberryPiAarch64`, covers the
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64-bit boards (Pi 3/4/5). For a 32-bit board, override this with the
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matching U-Boot package.
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'';
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};
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};
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useGenerationDeviceTree = lib.mkOption {
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type = lib.types.bool;
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default = false;
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description = ''
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Copy device trees from the booted NixOS generation
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(`/run/current-system/dtbs`) instead of the vendor firmware package.
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Irrelevant when generating an SD image.
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'';
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};
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};
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config = lib.mkMerge [
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(lib.mkIf cfg.uboot.enable {
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# Chainload U-Boot: the GPU firmware loads u-boot.bin, which then reads
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# extlinux.conf. mkDefault so an explicit kernel setting still wins.
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hardware.raspberry-pi.configtxt.settings.all = {
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kernel = lib.mkDefault "u-boot.bin";
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# Default U-Boot is 64-bit, but the firmware loads kernel= in 32-bit
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# mode unless arm_64bit=1.
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arm_64bit = lib.mkDefault pkgs.stdenv.hostPlatform.isAarch64;
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};
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# The GPU firmware merges config.txt dtoverlays into the DTB it hands to
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# U-Boot. The default (true) adds an FDTDIR line to extlinux.conf, so
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# U-Boot reloads bare dtbs and drops the overlays.
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boot.loader.generic-extlinux-compatible.useGenerationDeviceTree = lib.mkDefault false;
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})
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# Stage the firmware partition at SD-image build time, only when an
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# sd-image module is imported. mkForce so we override (not merge with)
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# sd-image-aarch64.nix, which also sets this and would clobber config.txt.
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(lib.optionalAttrs (options ? sdImage) {
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sdImage.populateFirmwareCommands = lib.mkForce "${lib.getExe installScript} ./firmware\n";
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})
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(lib.mkIf cfg.enable {
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system.activationScripts.raspberry-pi-firmware = lib.stringAfter [ "specialfs" ] ''
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if mountpoint -q ${lib.escapeShellArg cfg.path}; then
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${lib.getExe installScript} ${lib.escapeShellArg cfg.path}
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else
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echo "rpi-firmware: ${cfg.path} is not a mounted partition, skipping firmware install" >&2
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fi
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'';
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})
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];
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}
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