How to Install Custom dts/dtbo?

[hftsai256]

I'm seeking a way to build a Raspberry Pi CM4 image with several customized dts/dtbo, e.g. mcp4728.dts. My first intuition is something like this:

hardware.deviceTree = {
  kernelPackage = pkgs.linux_rpi4;
  filter = "bcm2711-rpi-cm4.dtb";
  overlays = [
    { name = "mcp4728"; dtsFile = ./mcp4728.dts; }
    { name = "spi6-1cs"; dtboFile = "${pkgs.device-tree_rpi.overlays}/spi6-1cs.dtbo"; }
  ];
};

But then I find boot.loader.generic-extlinux-compatible.useGenerationDeviceTree = false, and I doubt the path I'm taking will be effective.

My another thought is to create a separate Nix package to handle the build/install part:

{ stdenvNoCC, dtc }:
stdenvNoCC.mkDerivation {
  pname = "dtoverlays";
  version = "0.0.1";
  src = ./.;
  buildInputs = [ dtc ];
  installPhase = ''
    install -d $out/boot/firmware/overlays
    mv build/*.dtbo $out/boot/firmware/overlays
  '';
}

However as far as I concerned, the install path /boot/firmware/overlays is in a different partition from rootfs, and therefore I also doubt that I can include this package in environment.systemPackages

Is there a way to build the dtbo from source and install them into /boot/firmware/overlays?

[tstat]

Hey @hftsai256. The short answer to your question is that overlays are taken from the package raspberrypifw, so you could override that to add an overlay. This is mentioned in the readme under this section.

Reading the firmware populating script might clarify how this all fits together in your mind. Specifically, the device tree overlays are populated here.