regression in drm_blank.c?

[Steve French]

For the last month my logs have been flooded many times a second with:

"nouveau 0000:01:00.0: [drm] *ERROR* crtc 50: Can't calculate
constants, dotclock = 0!"

(see line 641 of drm_vblank.c) which is distracting for debugging all
other kernel problems (since dmesg entries on this system are 99+%
this message).

Am running current kernel ie 5.11-rc5 (although it also was very very
noisty in 5.10), Ubuntu mainline kernel builds, Lenovo P52 Thinkpad
laptop.  Could it be due to one of the more recent changes to
drivers/gpu/drm/drm_vblank.c?

Ideas how to workaround this?

-- 
Thanks,

Steve