Raspberry Pi 4 device tree overlay not applied / generic-extlinux-compatible.enable not working?

[SFrijters]

Due to NixOS/nixpkgs#241534 I've been trying to migrate my config to something more future compatible.

In particular I've tried to move from

dtparam=eth_led0=4
dtparam=eth_led1=4

in /boot/config.txt via boot.loader.raspberryPi.firmwareConfig to an overlay

+      {
+        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>;
+                  };
+              };
+          };
+        '';
+      }

in hardware.deviceTree.overlays.

When I decompile the bcm2711-rpi-4-b.dtb file in /boot/nixos/...-device-tree-overlays with and without the overlay I can see the diff

--- with-overlay.txt    2023-10-14 12:32:37.517621679 +0200
+++ without-overlay.txt 2023-10-14 12:33:21.904783804 +0200
@@ -2150,7 +2150,7 @@

                                ethernet-phy@1 {
                                        reg = <0x01>;
-                                       led-modes = <0x04 0x04>;
+                                       led-modes = <0x00 0x08>;
                                        phandle = <0x2f>;
                                };

However, after rebooting the LEDs stay on and I can inspect

$ hexdump /proc/device-tree/scb/ethernet@7d580000/mdio@e14/ethernet-phy@1/led-modes 
0000000 0000 0000 0000 0800                    
0000008

Any idea why this isn't correct? https://forums.raspberrypi.com/viewtopic.php?t=357717 suggests my overlay is correct, so I now suspect it's a problem with how I'm doing things in a NixOS context.

I'm using the nixos-hardware module and hardware.raspberry-pi."4".apply-overlays-dtmerge.enable = true;.

[SFrijters]

Ah, it looks like the migration to generic-extlinux-compatible.enable = true; is more involved maybe?
When I use nixos rebuild-switch new entries are added to /boot/extlinux, but the /run/current-system link is still pointing to the system configuration I started out with this morning.

What is the correct way to migrate this?

[SFrijters]

Solved via discussion in NixOS/nixpkgs#241534 and related PRs.