RockPro64 linux console video mode

I have a weird issue with the linux console.  I am trying to setup a rockpro64 and in doing that I am using an old Dell monitor with a 1680x1050 resolution.

When the rockpro64 boots, the first thing that I see is the output from uboot. This is OK. Then linux is booted and for a short time I see a patterned screen. After this, there is the linux boot output.

The issue is that as soon as uboot gives control to the linux kernel, the display becomes terrible: all trembling and slightly distorted. The monitor reports that the output is at 1400x1050@55Hz, which is obviously not correct. However, /sys/class/graphics/fb0/modes correctly shows U:1680x1050p-0.

Obviously, I suspect that the poor display is due to using an output format that is not suited for the monitor. However:
  • Why does uboot pick the right display mode and linux does not?
  • What would be the proper way to instruct linux to use a more correct display mode for its console?

Note that the issue seems to be cross-distro (tested with debian and manjaro).

Thanks for any help,

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