Confused about i915kms on 12.1

[Chuck Tuffli]

I've been running 12.0-REL on my X1 Carbon 3rd Gen happily with xorg,
but after installing 12.1-RC1, the laptop reboots when loading the
i915kms driver. If I comment out the line in /etc/rc.conf:

kld_list="/boot/modules/i915kms.ko"

the laptop boots, albeit without graphics. The above comes from the
12.0R release notes, and I didn't see any updates to this in the 12.1
release notes. I've tried drm-kmod from both ports and packages with
the same result. Did something change with 12.1? What should I check?
TIA

--chuck