Boot messages scroll off bottom of screen on ThinkPad T580 with drm-next-kmod-20180822

[Rebecca Cran]

I'm not sure when this started, but I've recently updated my kernel to
r338669 (12.0-ALPHA5) and am running drm-next-kmod-4.11-g20180822on a
ThinkPad T530. Now when I boot, after the i915kms.ko loads the boot
messages start scrolling off the bottom of the screen, and I can only
see them by hitting Enter lots of times. As suggested on gitter.im I
tried running drm-devel-kmod, but it caused the screen to blank and the
machine to apparently hang (as in
https://lists.freebsd.org/pipermail/freebsd-x11/2018-September/021588.html,
but the caps lock key on the built-in keyboard kept working).

This is the dmesg from loading drm-next-kmod:

drmn0: <drmn> on vgapci0
vgapci0: child drmn0 requested pci_enable_io
vgapci0: child drmn0 requested pci_enable_io
[drm] Memory usable by graphics device = 4096M
Failed to add WC MTRR for [0xc0000000-0xcfffffff]: -22; performance may
suffer
[drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[drm] Driver supports precise vblank timestamp query.
[drm] DMC: load work fn start
i915/kbl_dmc_ver1_01.bin: could not load firmware image, error 2
[drm] Connector eDP-1: get mode from tunables:
[drm]   - kern.vt.fb.modes.eDP-1
[drm]   - kern.vt.fb.default_mode
i915/kbl_dmc_ver1_01.bin: could not load firmware image, error 2
[drm] Finished loading DMC firmware i915/kbl_dmc_ver1_01.bin (v1.1)
[drm] DMC: load work fn end
[drm] Connector DP-1: get mode from tunables:
[drm]   - kern.vt.fb.modes.DP-1
[drm]   - kern.vt.fb.default_mode
[drm] Connector HDMI-A-1: get mode from tunables:
[drm]   - kern.vt.fb.modes.HDMI-A-1
[drm]   - kern.vt.fb.default_mode
[drm] Connector DP-2: get mode from tunables:
[drm]   - kern.vt.fb.modes.DP-2
[drm]   - kern.vt.fb.default_mode
[drm] Connector HDMI-A-2: get mode from tunables:
[drm]   - kern.vt.fb.modes.HDMI-A-2
[drm]   - kern.vt.fb.default_mode
i915/kbl_huc_ver02_00.bin: could not load firmware image, error 2
i915/kbl_huc_ver02_00.bin: could not load firmware image, error 2
[drm] GuC firmware load skipped
[drm] Initialized i915 1.6.0 20170123 for drmn0 on minor 0
VT: Replacing driver "efifb" with new "fb".
[drm] Connector DP-3: get mode from tunables:
[drm]   - kern.vt.fb.modes.DP-3
[drm]   - kern.vt.fb.default_mode
start FB_INFO:
type=11 height=2160 width=3840 depth=32
cmsize=16 size=33177600
pbase=0xc0040000 vbase=0xfffff800c0040000
name=drmn0 flags=0x0 stride=15360 bpp=32
cmap[0]=0 cmap[1]=7f0000 cmap[2]=7f00 cmap[3]=c4a000
end FB_INFO
drmn0: fb0: inteldrmfb frame buffer device
lo0: link state changed to UP
[drm] Connector DP-4: get mode from tunables:
[drm]   - kern.vt.fb.modes.DP-4
[drm]   - kern.vt.fb.default_mode
[drm] Connector DP-5: get mode from tunables:
[drm]   - kern.vt.fb.modes.DP-5
[drm]   - kern.vt.fb.default_mode

-- 
Rebecca Cran