Thank you for confirming that the RPi4 Ethernet setup is still a To-Do in U-Boot. Now would it make sense to bring this feature to attention on the U-Boot mailing list? Most likely someone with the required skill will pick this up sooner or later regardless, but wishful thinking on my behalf suggest...

Excellent job, agherzan! Can't wait to test this on my lab RPi4 and eventually seeing it upstreamed! I'm primarily interested in using U-Boot to netboot a kernel/initrd via Ethernet, with just U-Boot and the firmware blobs residing on the SD card, this already works beautifully on RPi2/3. I understa...