Exactly. After days of unsuccessful VideoBIOS bring-up (via U-Boot's emulator), I gave up, and implemented exactly what you suggested: graphics mode, using of course parts of nouveau. Claude Code is smart in extracting information.

And it worked!! Now I have the picture on the monitor when U-Boot starts. The only one drawback: it takes 30..40 seconds between the moment of machine-power-on and the picture on the screen.