Brightness cannot be set on Lenovo L15 ThinkPad

[Pete Wright]

On 2/9/21 9:31 PM, Kevin Oberman wrote:
> 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!

Hey there Kevin,
I have a Thinkpad P43s with working backlight - on my end I load the 
both the acpi_ibm and acpi_video kernel modules.  One interesting nit is 
that I have to load the ibm kmod *before* the video kmod or things don't 
work.  Here's my kld_list from rc.conf:

kld_list="cpuctl /boot/modules/i915kms.ko acpi_ibm acpi_video filemon"

i also set my default brightness via sysctl.conf like so:
hw.acpi.video.lcd0.brightness=40

My reading of the man pages is that acpi_ibm is used to enable the 
function keys to control brightness, volume control etc and acpi_video 
does manages the backlight brightness itself.

Hope this helps,
-pete

-- 
Pete Wright
pete at nomadlogic.org
@nomadlogicLA