modify live DT with OF_LIVE breaking phy_connect?

[Tim Harvey]

Greetings,

I have a need to adjust the U-Boot device-tree live with some board
revision specific fixups. It would seem I need to enable OF_LIVE to do
so but when I do this on imx8mm U-Boot proper seems to fail
phy_connect() called from the network device probe.

The board I'm working with is an imx8mm-venice board and using
imx8mm_venice_defconfig (without OF_LIVE) results in:
U-Boot 2024.10-00735-gc530f6079c70 (Oct 07 2024 - 12:58:38 -0700)

CPU:   Freescale i.MX8MMQ rev1.0 1600 MHz (running at 1200 MHz)
CPU:   Industrial temperature grade (-40C to 105C) at 44C
Reset cause: POR
Model: Gateworks Venice GW73xx-0x i.MX8MM Development Kit
DRAM:  4 GiB
Core:  226 devices, 32 uclasses, devicetree: separate
WDT:   Started watchdog at 30280000 with servicing every 1000ms (60s timeout)
MMC:   FSL_SDHC: 0, FSL_SDHC: 1, FSL_SDHC: 2
Loading Environment from MMC... Reading from redundant MMC(2)... OK
In:    serial at 30890000
Out:   serial at 30890000
Err:   serial at 30890000
SEC0:  RNG instantiated
Net:   GPY111 eth0: ethernet at 30be0000 [PRIME]
GSC     : boot watchdog disabled
Thermal protection:enabled at 96C
Hit any key to stop autoboot:  0

Yet as soon as I enable OF_LIVE:

U-Boot 2024.10-00735-gc530f6079c70 (Oct 07 2024 - 12:59:35 -0700)

CPU:   Freescale i.MX8MMQ rev1.0 1600 MHz (running at 1200 MHz)
CPU:   Industrial temperature grade (-40C to 105C) at 49C
Reset cause: POR
Model: Gateworks Venice GW73xx-0x i.MX8MM Development Kit
DRAM:  4 GiB
Core:  214 devices, 32 uclasses, devicetree: separate
WDT:   Started watchdog at 30280000 with servicing every 1000ms (60s timeout)
MMC:   FSL_SDHC: 0, FSL_SDHC: 1, FSL_SDHC: 2
Loading Environment from MMC... Reading from redundant MMC(2)... OK
In:    serial at 30890000
Out:   serial at 30890000
Err:   serial at 30890000
SEC0:  RNG instantiated
Net:   Could not get PHY for mdio: addr 0
Could not get PHY for FEC0: addr 0
Could not get PHY for mdio: addr 0
Could not get PHY for FEC0: addr 0
No ethernet found.
^^^ phy_connect failing

Any idea what I'm missing here?

Are there other ways I should be modifying the live dt in U-Boot?

Best Regards,

Tim