This update produces reams of these messages on my system:

Apr 05 09:17:36 Gertrud kernel: [drm] Reducing the compressed framebuffer size.
This may lead to less power savings than a non-reduced-size. Try to increase
stolen memory size if available in BIOS.

There is no BIOS setting I could change on my Dell T20 unfortunaltely.

I have already tried to set the kernel parameter i915.enable_fbc=0 (and
a parameter file in /etc/modprobe.d with the same settings), which does
result in a tainted kernel (so the setting should be active), but these
messages still continue at a high rate and the frambuffer compression
seems to be enabled anyway.

The 5.5.* kernels do not have this problem, this message never occurs
there.