Cannot boot imx8mm symphony board

[Denis Benato <benato.denis96@gmail.com>]

Hello,

I write this to ask for help in booting linux on a slight variation of the development board imx8mm-var-symphony.

At the moment I am using an u-boot version that can boot a linux 6.6 kernel and a 5.15.60 that I have
adapted to my custom board: https://github.com/NeroReflex/linux-imx/tree/old

I can boot that without any problem: the gpu works as well as networking, backlight, RTC and every other device on the board; however I want to use either 6.14.4 or linux-next.

On that version I can see a device tree arch/arm64/boot/dts/freescale/imx8mm-var-som-symphony.dts
that, from my understanding, is supposed to at least arrive at the point of printing something from the debug serial, where I can actually pick up and start figuring out what's missing/wrong.

My problem is that u-boot (the same u-boot version that can boot v6.6 just fine) works flawlessly, the fdt is
loaded into memory as well as the kernel, but then I have no output on the debug serial, no backlight is turned on (I tried adding my screen to the device tree) and the ethernet controller on my board does not reset as
it usually does when a working kernel is booted: this lead me into thinking there is a problem somewhere in
the early boot sequence.

Therefore I attempted to use the previously working device tree, the one from 5.15, but to no avail.

At this time I think my problem can only be either one of these:
- u-boot I am using is not suitable to boot kernels past 6.6

- I have a problem in my config

I also tried using the following patch as it appears to be relevant for this hardware:

https://lore.kernel.org/all/20250311-wip-obbardc-qcom-defconfig-interconnects-builtin-v1-1-675b6bc57176@linaro.org

but again to no avail.

Can someone please point me in the right direction? What config am I supposed to be using to boot that board?
What version of u-boot (and configuration) should I be using?

Thanks in advice,
Denis