Brightness cannot be set on Lenovo L15 ThinkPad

[Kevin Oberman]

I can only guess that this may be an ACPI issue.

I recently (last week) replaced my decade old T520 with a new ThinkPad L15
with a 10th gen I5 CPU (Tiger Lake). I have everything working except the
WiFi (which I knew would not work) and setting brightness on the display.

I have loaded acpi_ibm and it returns '0' for brightness. I tried
intel-backlight, which shows the brightness to be '0'. It does nothing,
either.

I thought that I read that drm-fbsd13-kmod had the ability to do the job,
but I have no idea how to do anything with it. I do see sysctls for
hw.i915kms.enable_dpcd_backlight and invert_brightness, but I still have no
clue whether they are relevant.

Any suggestions would be greatly appreciated!
--
Kevin Oberman, Part time kid herder and retired Network Engineer
E-mail: rkoberman at gmail.com
PGP Fingerprint: D03FB98AFA78E3B78C1694B318AB39EF1B055683