Device tree overlays to disable LEDs on a Raspberry Pi 4

configuration.nix

  hardware.deviceTree = {
    enable = true;

    # Use source-based overlays so they are compatible with the kernel and hardware
    # Based on:
    #   * "Device trees" documentation in https://www.raspberrypi.com/documentation/computers/configuration.html#part1,
    #   * arch/arm/boot/dts/bcm2711-rpi-4-b.dts in https://github.com/raspberrypi/linux
    #   * Example files in arch/arm/boot/dts/overlays
    #
    # For debugging:
    # $ nix-shell -p dtc
    # $ nix build /persist/etc/nixos#nixosConfigurations.phellack.config.hardware.deviceTree.package -L
    # $ fdtget -t s ./result/broadcom/bcm2711-rpi-4-b.dtb / compatible
    # $ dtc -I dtb -O dts ./result/broadcom/bcm2711-rpi-4-b.dtb | less

    overlays = [
      # Based on disable-wifi-overlay.dts
      {
        name = "disable-wifi";
        filter = "*rpi-4-b*";
        dtsText = ''
          /dts-v1/;
          /plugin/;
          /{
              compatible = "raspberrypi,4-model-b";
              fragment@0 {
                  target = <&mmc>;
                  __overlay__ {
                      status = "disabled";
                  };
              };

              fragment@1 {
                  target = <&mmcnr>;
                  __overlay__ {
                      status = "disabled";
                  };
              };
          };
        '';
      }
      # Based on disable-bt-overlay.dts
      {
        name = "disable-bt";
        filter = "*rpi-4-b*";
        dtsText = ''
          /dts-v1/;
          /plugin/;
          /{
              compatible = "raspberrypi,4-model-b";
              fragment@0 {
                  target = <&bt>;
                  __overlay__ {
                      status = "disabled";
                  };
              };
          };
        '';
      }
      # https://github.com/raspberrypi/firmware/blob/master/boot/overlays/README
      # eth_led0                Set mode of LED0 - amber on Pi3B+ (default "1"),
      #                         green on Pi4 (default "0").
      #                         The legal values are:
      #
      #                         Pi4
      #
      #                         0=Speed/Activity         1=Speed
      #                         2=Flash activity         3=FDX
      #                         4=Off                    5=On
      #                         6=Alt                    7=Speed/Flash
      #                         8=Link                   9=Activity
      #
      # Debugging:
      # $ hexdump /proc/device-tree/scb/ethernet@7d580000/mdio@e14/ethernet-phy@1/led-modes
      {
        name = "disable-eth-leds";
        filter = "*rpi-4-b*";
        dtsText = ''
          /dts-v1/;
          /plugin/;
          /{
             compatible = "raspberrypi,4-model-b";
             fragment@0 {
                  target = <&phy1>;
                  __overlay__ {
                      led-modes = <0x04 0x04>;
                  };
              };
          };
        '';
      }
      # Debugging:
      # $ hexdump /proc/device-tree/leds/led-act/gpios
      # $ cat /proc/device-tree/leds/led-act/linux,default-trigger
      {
        name = "disable-act-led";
        filter = "*rpi-4-b*";
        dtsText = ''
          /dts-v1/;
          /plugin/;
          /{
              compatible = "raspberrypi,4-model-b";
              fragment@0 {
                  target = <&act_led>;
                  __overlay__ {
                      gpios = <&gpio 42 0>; /* first two values copied from bcm2711-rpi-4-b.dts */
                      linux,default-trigger = "none";
                  };
              };
          };
        '';
      }
      # Debugging:
      # $ hexdump /proc/device-tree/leds/led-pwr/gpios
      # $ cat /proc/device-tree/leds/led-pwr/linux,default-trigger
      {
        name = "disable-pwr-led";
        filter = "*rpi-4-b*";
        dtsText = ''
          /dts-v1/;
          /plugin/;
          /{
              compatible = "raspberrypi,4-model-b";
              fragment@0 {
                  target = <&pwr_led>;
                  __overlay__ {
                      gpios = <&expgpio 2 0>; /* first two values copied from bcm2711-rpi-4-b.dts */
                      linux,default-trigger = "default-on";
                  };
              };
          };
        '';
      }
    ];
  };