NixOS on Samsung Chromebook Plus

This project is a configuration of NixOS that renders it bootable on a Samsung Chromebook Plus in the form of a image that can be dumped to a microSD card and booted directly. The majority of the effort was accomplished by the Arch Linux ARM project, which builds an appropriate kernel, which was imported directly.

Status

Weekend hobby project. Works for me.

Building

nix-build release.nix -A sdImage

Or try ./simple-build.sh.

Installation

1. Place device in Developer Mode
2. Dump image to SD card.
3. Insert into Chromebook.
4. Boot with Ctrl-U.

Post installation configuration

Use the standard nixos-generate-config command to generate the hardware and filesystem configuration file. In the main configuration file (configuration.nix), include the two modules from this repository's modules/ directory, which adds in the kernel package, and the depthcharge bootloader integration. In you main configuration.nix, specify your desired kernel. For example:

{ config, lib, pkgs, ... }:
{
  include = [
    ./kevin-nix/modules
  ];

  boot.kernelPackages = pkgs.linuxPackages_gru_4_4;

  boot.loader.depthcharge.enable = true;
  boot.loader.depthcharge.partition = "/dev/disk/by-partlabel/kernel";
}

nixos-rebuild switch

The boot process scans the media for a partition designated as a kernel, using attributes stored in GPT.

This kernel partition (kpart) is a Flattened Image Tree (fit) image including the kernel, a set of dtbs, the initrd, and the kernel command line.

The depthcharge module will will produce a kernel partition (kpart) file as part of the toplevel system, and on switch will write its contents to the kernel partition.

The kernel partition is not a GC root. If you remove old versions of your system profile, you may render your environment unbootable.

Generated partition layout

$(nix-build --no-out-link -E 'import <nixpkgs> { overlays = [ (import ./packages) ]; }' -A vboot_reference)/bin/cgpt show $(readlink -f ./result/sd-image/*.img)

       start        size    part  contents
           0           1          PMBR
           1           1          Pri GPT header
           2          32          Pri GPT table
        2048      131072       1  Label: "kernel"
                                  Type: ChromeOS kernel
                                  UUID: 534078AF-3BB4-EC43-B6C7-828FB9A788C6
                                  Attr: priority=10 tries=5 successful=1
      133120     4393031       2  Label: "NIX_SD"
                                  Type: B921B045-1DF0-41C3-AF44-4C6F280D3FAE
                                  UUID: 0340EA1D-C827-8048-B631-0C60D4478796
     4526151          32          Sec GPT table
     4526183           1          Sec GPT header

Notice the additional metadata for the kernel partition Attr: priority=10 tries=5 successful=1.

Versions

Tested against nixpkgs f607771d0f5.

Future work

• Make a fit image containing uboot, which can then use the standard extlinux-based boot flow.

• Use a vanilla kernel. It is expected that 4.16 will include support that enables the display without additional patches.

• Use depthcharge's fallback features to have multiple bootable profiles.

• Build the open source Mali kernel module from ARM that matches the binary libmali.so available from rockchip.