configuration.nix/hosts/rico1/hardware/default.nix

{ lib, ... }: {
  imports = [ ./filesystem.nix ./kernel.nix ];

  #hardware.raspberry-pi."4".poe-plus-hat.enable = true;
  hardware.raspberry-pi."4".apply-overlays-dtmerge.enable = lib.mkDefault true;
  hardware.deviceTree.filter = "bcm2711-rpi-4*.dtb";
  hardware.deviceTree = {
    overlays = [
      # Combined equivalent to:
      # * https://github.com/raspberrypi/linux/blob/rpi-6.1.y/arch/arm/boot/dts/overlays/rpi-poe-overlay.dts
      # * https://github.com/raspberrypi/linux/blob/rpi-6.1.y/arch/arm/boot/dts/overlays/rpi-poe-plus-overlay.dts
      {
        name = "rpi-poe-plus-overlay";
        dtsText = ''
          /*
          * Overlay for the Raspberry Pi POE HAT.
          */
          /dts-v1/;
          /plugin/;

          / {
            compatible = "brcm,bcm2711";

            fragment@0 {
              target-path = "/";
              __overlay__ {
                fan: pwm-fan {
                  compatible = "pwm-fan";
                  cooling-levels = <0 1 10 100 255>;
                  #cooling-cells = <2>;
                  pwms = <&fwpwm 0 80000>;
                };
              };
            };

            fragment@1 {
              target = <&cpu_thermal>;
              __overlay__ {
                polling-delay = <2000>; /* milliseconds */
              };
            };

            fragment@2 {
              target = <&thermal_trips>;
              __overlay__ {
                trip0: trip0 {
                  temperature = <55000>;
                  hysteresis = <2000>;
                  type = "active";
                };
                trip1: trip1 {
                  temperature = <58000>;
                  hysteresis = <2000>;
                  type = "active";
                };
                trip2: trip2 {
                  temperature = <61000>;
                  hysteresis = <2000>;
                  type = "active";
                };
                trip3: trip3 {
                  temperature = <64000>;
                  hysteresis = <5000>;
                  type = "active";
                };
              };
            };

            fragment@3 {
              target = <&cooling_maps>;
              __overlay__ {
                map0 {
                  trip = <&trip0>;
                  cooling-device = <&fan 0 1>;
                };
                map1 {
                  trip = <&trip1>;
                  cooling-device = <&fan 1 2>;
                };
                map2 {
                  trip = <&trip2>;
                  cooling-device = <&fan 2 3>;
                };
                map3 {
                  trip = <&trip3>;
                  cooling-device = <&fan 3 4>;
                };
              };
            };

            fragment@4 {
              target-path = "/__overrides__";
              params: __overlay__ {
                poe_fan_temp0 =		<&trip0>,"temperature:0";
                poe_fan_temp0_hyst =	<&trip0>,"hysteresis:0";
                poe_fan_temp1 =		<&trip1>,"temperature:0";
                poe_fan_temp1_hyst =	<&trip1>,"hysteresis:0";
                poe_fan_temp2 =		<&trip2>,"temperature:0";
                poe_fan_temp2_hyst =	<&trip2>,"hysteresis:0";
                poe_fan_temp3 =		<&trip3>,"temperature:0";
                poe_fan_temp3_hyst =	<&trip3>,"hysteresis:0";
                poe_fan_i2c =		<&fwpwm>,"status=disabled",
                      <&poe_mfd>,"status=okay",
                      <&fan>,"pwms:0=",<&poe_mfd_pwm>;
              };
            };

            fragment@5 {
              target = <&firmware>;
              __overlay__ {
                fwpwm: pwm {
                  compatible = "raspberrypi,firmware-poe-pwm";
                  #pwm-cells = <2>;
                };
              };
            };

            fragment@6 {
              target = <&i2c0>;
              i2c_bus: __overlay__ {
                #address-cells = <1>;
                #size-cells = <0>;

                poe_mfd: poe@51 {
                  compatible = "raspberrypi,poe-core";
                  reg = <0x51>;
                  status = "disabled";

                  poe_mfd_pwm: poe_pwm@f0 {
                    compatible = "raspberrypi,poe-pwm";
                    reg = <0xf0>;
                    status = "okay";
                    #pwm-cells = <2>;
                  };
                };
              };
            };

            fragment@7 {
              target = <&i2c0if>;
              __dormant__ {
                status = "okay";
              };
            };

            fragment@8 {
              target = <&i2c0mux>;
              __dormant__ {
                status = "okay";
              };
            };

            __overrides__ {
              poe_fan_temp0 =		<&trip0>,"temperature:0";
              poe_fan_temp0_hyst =	<&trip0>,"hysteresis:0";
              poe_fan_temp1 =		<&trip1>,"temperature:0";
              poe_fan_temp1_hyst =	<&trip1>,"hysteresis:0";
              poe_fan_temp2 =		<&trip2>,"temperature:0";
              poe_fan_temp2_hyst =	<&trip2>,"hysteresis:0";
              poe_fan_temp3 =		<&trip3>,"temperature:0";
              poe_fan_temp3_hyst =	<&trip3>,"hysteresis:0";
              i2c =			<0>, "+5+6",
                    <&fwpwm>,"status=disabled",
                    <&i2c_bus>,"status=okay",
                    <&poe_mfd>,"status=okay",
                    <&fan>,"pwms:0=",<&poe_mfd_pwm>;
            };
          };

          // SPDX-License-Identifier: (GPL-2.0 OR MIT)
          // Overlay for the Raspberry Pi PoE+ HAT.

          / {
            compatible = "brcm,bcm2711";

            fragment@10 {
              target-path = "/";
              __overlay__ {
                rpi_poe_power_supply: rpi-poe-power-supply {
                  compatible = "raspberrypi,rpi-poe-power-supply";
                  firmware = <&firmware>;
                  status = "okay";
                };
              };
            };
            fragment@11 {
              target = <&poe_mfd>;
              __overlay__ {
                rpi-poe-power-supply@f2 {
                  compatible = "raspberrypi,rpi-poe-power-supply";
                  reg = <0xf2>;
                  status = "okay";
                };
              };
            };

            __overrides__ {
              i2c =	<0>, "+5+6",
                <&fwpwm>,"status=disabled",
                <&rpi_poe_power_supply>,"status=disabled",
                <&i2c_bus>,"status=okay",
                <&poe_mfd>,"status=okay",
                <&fan>,"pwms:0=",<&poe_mfd_pwm>;
            };
          };

          &fan {
            cooling-levels = <0 32 64 128 255>;
          };

          &params {
            poe_fan_i2c = <&fwpwm>,"status=disabled",
                    <&rpi_poe_power_supply>,"status=disabled",
                    <&poe_mfd>,"status=okay",
                    <&fan>,"pwms:0=",<&poe_mfd_pwm>;
          };
        '';
      }
    ];
  };
}