The last patch helps, no more messages and the computer doesn't hang completely
for several seconds (I wouldn't exactly say that's harmless ;-) ). Thanks for
the fix !

I detected a few different error messages when checking dmesg:
[drm:radeon_atom_get_leakage_vddc_based_on_leakage_params] *ERROR* Unknown
table version 3, 1

Do those warrant a new bugreport ?