Sorry for the late reply. I finally found the time and HW to test this.
But it works just fine for me. The overlay is loaded by the FW, the fan
spins up and down, ...
root@rpi-4b-rev1d1-17cf:/home/ubuntu# uname -a
Linux rpi-4b-rev1d1-17cf 5.13.0-1008-raspi #9-Ubuntu SMP PREEMPT Wed Sep 29
08:27:44 UTC 2021 aarch64 aarch64 aarch64 GNU/Linux
root@rpi-4b-rev1d1-17cf:/home/ubuntu# ./vcdbg log msg
005358.526: arasan: arasan_emmc_open
005799.047: brfs: File read: /mfs/sd/config.txt
005801.892: brfs: File read: 1003 bytes
005810.420: brfs: File read: /mfs/sd/install/config.txt
005813.953: brfs: File read: 182 bytes
005936.890: HDMI1:EDID error reading EDID block 0 attempt 0
005946.406: HDMI1:EDID error reading EDID block 0 attempt 1
005955.916: HDMI1:EDID error reading EDID block 0 attempt 2
005965.430: HDMI1:EDID error reading EDID block 0 attempt 3
005974.937: HDMI1:EDID error reading EDID block 0 attempt 4
005984.451: HDMI1:EDID error reading EDID block 0 attempt 5
005993.960: HDMI1:EDID error reading EDID block 0 attempt 6
006003.474: HDMI1:EDID error reading EDID block 0 attempt 7
006012.982: HDMI1:EDID error reading EDID block 0 attempt 8
006022.496: HDMI1:EDID error reading EDID block 0 attempt 9
006026.997: HDMI1:EDID giving up on reading EDID block 0
006033.577: brfs: File read: /mfs/sd/config.txt
007144.477: gpioman: gpioman_get_pin_num: pin DISPLAY_DSI_PORT not defined
007151.770: *** Restart logging
007153.193: brfs: File read: 1003 bytes
007221.534: hdmi: HDMI1:EDID error reading EDID block 0 attempt 0
007231.567: hdmi: HDMI1:EDID error reading EDID block 0 attempt 1
007245.266: hdmi: HDMI1:EDID error reading EDID block 0 attempt 2
007255.356: hdmi: HDMI1:EDID error reading EDID block 0 attempt 3
007265.451: hdmi: HDMI1:EDID error reading EDID block 0 attempt 4
007275.536: hdmi: HDMI1:EDID error reading EDID block 0 attempt 5
007285.631: hdmi: HDMI1:EDID error reading EDID block 0 attempt 6
007295.720: hdmi: HDMI1:EDID error reading EDID block 0 attempt 7
007305.815: hdmi: HDMI1:EDID error reading EDID block 0 attempt 8
007315.901: hdmi: HDMI1:EDID error reading EDID block 0 attempt 9
007320.978: hdmi: HDMI1:EDID giving up on reading EDID block 0
007331.632: hdmi: HDMI1:EDID error reading EDID block 0 attempt 0
007341.718: hdmi: HDMI1:EDID error reading EDID block 0 attempt 1
007351.814: hdmi: HDMI1:EDID error reading EDID block 0 attempt 2
007361.903: hdmi: HDMI1:EDID error reading EDID block 0 attempt 3
007371.998: hdmi: HDMI1:EDID error reading EDID block 0 attempt 4
007382.083: hdmi: HDMI1:EDID error reading EDID block 0 attempt 5
007392.177: hdmi: HDMI1:EDID error reading EDID block 0 attempt 6
007402.267: hdmi: HDMI1:EDID error reading EDID block 0 attempt 7
007412.362: hdmi: HDMI1:EDID error reading EDID block 0 attempt 8
007422.447: hdmi: HDMI1:EDID error reading EDID block 0 attempt 9
007427.525: hdmi: HDMI1:EDID giving up on reading EDID block 0
007433.128: hdmi: HDMI:hdmi_get_state is deprecated, use hdmi_get_display_state
instead
007441.885: HDMI0: hdmi_pixel_encoding: 3
007447.350: HDMI1: hdmi_pixel_encoding: 3
011373.662: brfs: File read: /mfs/sd/initrd.img
011376.173: Loading 'initrd.img' to 0x0 size 0x1259e13
011410.516: initramfs loaded to 0x2dda6000 (size 0x1259e13)
011438.407: dtb_file 'bcm2711-rpi-4-b.dtb'
011440.481: brfs: File read: 19242515 bytes
011456.816: brfs: File read: /mfs/sd/bcm2711-rpi-4-b.dtb
011460.105: Loading 'bcm2711-rpi-4-b.dtb' to 0x100 size 0xc35d
011498.256: brfs: File read: 50013 bytes
011506.178: brfs: File read: /mfs/sd/overlays/overlay_map.dtb
011662.776: brfs: File read: 1667 bytes
011671.920: brfs: File read: /mfs/sd/overlays/rpi-poe-plus.dtbo
011700.115: Loaded overlay 'rpi-poe-plus'
011866.810: brfs: File read: 3262 bytes
011871.168: brfs: File read: /mfs/sd/config.txt
011874.065: dtparam: audio=on
011902.526: dtparam: i2c_arm=on
011925.403: dtparam: spi=on
011947.558: brfs: File read: 1003 bytes
011961.874: brfs: File read: /mfs/sd/overlays/dwc2.dtbo
011980.087: Loaded overlay 'dwc2'
012022.494: brfs: File read: 801 bytes
012025.597: brfs: File read: /mfs/sd/cmdline.txt
012029.644: Read command line from file 'cmdline.txt':
012035.498: 'net.ifnames=0 dwc_otg.lpm_enable=0 root=LABEL=writable
rootfstype=ext4 elevator=deadline rootwait fixrtc console=tty1
console=serial0,115200 ignore_loglevel'
012182.303: brfs: File read: 157 bytes
013006.156: brfs: File read: /mfs/sd/vmlinuz
013008.360: Loading 'vmlinuz' to 0x8 size 0x90d840
014371.593: Kernel relocated to 0x20
014373.445: Device tree loaded to 0x2dd99100 (size 0xcef1)
014381.405: uart: Set PL011 baud rate to 103448.30 Hz
014388.734: uart: Set PL011 baud rate to 103448.30 Hz
014388.775: uart: Baud rate change done...
014390.794: uart: Baud rate change done...
014414.984: gpioman: gpioman_get_pin_num: pin SDCARD_CONTROL_POWER not defined
019819.168: vchiq_core: vchiq_init_state: slot_zero = 0xea08, is_master = 1
019821.357: hdmi: HDMI:hdmi_get_state is deprecated
