Move Raspberry Pi 4 support to a module

modules/default.nix

@@ -3,5 +3,6 @@
 {
 	imports = [
 		./proxy.nix
+		./rpi4.nix
 	];
 }

modules/rpi4.nix

@@ -0,0 +1,43 @@
+{ config, lib, pkgs, ... }:
+
+let
+	cfg = config.greg.rpi4;
+
+in with lib; {
+	options = {
+		greg.rpi4 = {
+			enable = mkEnableOption "Enable support for Raspberry Pi 4s";
+		};
+	};
+
+	config = mkIf cfg.enable {
+		boot = {
+			# This prevents us from having to compile our own kernel
+			kernelPackages = pkgs.linuxPackages_rpi4;
+			kernelParams = [
+				"8250.nr_uarts=1"
+				"console=ttyAMA0,115200"
+				"console=tty1"
+				"cma=128M"
+			];
+
+			loader = {
+				raspberryPi = {
+					enable = true;
+					version = 4;
+				};
+
+				# Use the extlinux boot loader. (NixOS wants to enable GRUB by default)
+				grub.enable = false;
+
+				# Enables the generation of /boot/extlinux/extlinux.conf
+				#generic-extlinux-compatible.enable = true;
+			};
+		};
+
+		environment.systemPackages = with pkgs; [
+			raspberrypifw
+			usbutils
+		];
+	};
+}