Add device tree overlay for skycam

hosts/skycam/default.nix

@@ -10,16 +10,46 @@
     raspberry-pi."4" = {
       apply-overlays-dtmerge.enable = true;
       audio.enable = false;
-      fkms-3d.enable = true;    # VideoCore with 512 MB CMA reservation
-      tc358743.enable = true;   # HDMI-to-CSI-2 converter
       xhci.enable = false;
     };
+    deviceTree = {
+      enable = true;
+      filter = "*rpi-4-*.dtb";
+      # From https://github.com/Electrostasy/dots/blob/3b81723feece67610a252ce754912f6769f0cd34/hosts/phobos/klipper.nix#L43-L65
+      overlays =
+        let
+          mkCompatibleDtsFile = dtbo:
+            let
+              drv = pkgs.runCommand "fix-dts" { nativeBuildInputs = with pkgs; [ dtc gnused ]; } ''
+                mkdir "$out"
+                dtc -I dtb -O dts ${dtbo} | sed -e 's/bcm2835/bcm2711/' > $out/overlay.dts
+              '';
+            in
+              "${drv}/overlay.dts";
+
+          inherit (config.boot.kernelPackages) kernel;
+        in
+          [
+            {
+              name = "imx708.dtbo";
+              dtsFile = mkCompatibleDtsFile "${kernel}/dtbs/overlays/imx708.dtbo";
+            }
+            {
+              name = "vc4-kms-v3d-pi4.dtbo";
+              dtsFile = mkCompatibleDtsFile "${kernel}/dtbs/overlays/vc4-kms-v3d-pi4.dtbo";
+            }
+          ];
+    };
     firmware = with pkgs; [
       firmwareLinuxNonfree
       wireless-regdb
     ];
   };
 
+  services.udev.extraRules = ''
+    SUBSYSTEM="dma_heap", GROUP="video", MODE="0600"
+  '';
+
   networking = {
     hostId = "731d1660";
     firewall = {
@@ -61,6 +91,7 @@
   environment.systemPackages = with pkgs; [
     git
     neovim
+    libcamera
     libraspberrypi
     raspberrypi-eeprom
     v4l-utils

hosts/skycam/hardware-configuration.nix

@@ -7,10 +7,7 @@
 
   boot = {
     kernelModules = [ "bcm2835-v4l2" ];
-    loader.raspberryPi.firmwareConfig = ''
-      start_x=1
-      gpu_mem=256
-    '';
+    kernelParams = [ "cma=512M" ];
     supportedFilesystems = lib.mkForce [ "f2fs" "vfat xfs" ];
     tmp.cleanOnBoot = true;
   };