On my laptop the brightness doesn’t work anymore. Pressing Fn-F5 (brightness decrement) the brightness jump to 99% and then is not possible to regulate it: pressing Fn-F5 (brightness decrement) or Fn-F6 (brightness increment) the brightness is always at 99%.
I can regulate the brightness only with the intel_backlight program from the intel-backlight-20180328 package.
How can I reactivate the Fn functionality ?
Thanks in advance
Maurizio
Hi there @Maurizio,
welcome to the forum.
This is odd. Is the acpi_video module loaded (kldstat | grep acpi_video)?
Thank you for the for the quick answer.
The acpi_video module is loaded:
> kldstat | grep acpi_video
8 1 0xffffffff83219000 2b88 acpi_video.ko
Check whether acpi_ibm is loaded (kldstat | grep acpi_ibm). If not, load it as root:
kldload acpi_ibm
If that fixes the problem, add the line
acpi_ibm_load="YES"
to /boot/loader.conf to make it permanent.
I have solved disabling the acpi_video.ko driver (actually renaming it to acpi_video.ko.blacklisted) and rebooting the laptop.
But I have a question: what is the driver that controls the brightness?
P.S. Can an administrator correct the title in: “Lenovo T450 lost Fn brightness increment/decrement” ? Thanks.
Both, acpi_video and acpi_ibm, can control the brightness. Where acpi_video is a module which provides a generic interface for setting the brightness via ACPI, and ibm_acpi is a more device specific. I suspect that in your case, acpi_video, which also binds to the Fn+<brightness up/down> keys and is loaded first, doesn’t work correctly, and so the vendor specific acpi_ibm couldn’t get those key events.
The acpi_video(4) manpage refers to output switching, but it seems to be a similar problem:
BUGS Some systems only perform output switching via SMM even though they ex- port the proper information via ACPI. On such systems, the proper hotkeys or OEM driver (for example, acpi_toshiba(4)) must be used in- stead.
I have disabled ACPI_IBM(4) and ACPI_VIDEO(4) but the Fn brightness keys still work.
These drivers are loaded:
> kldstat
Id Refs Address Size Name
1 78 0xffffffff80200000 2448f20 kernel
2 1 0xffffffff82649000 3a9930 zfs.ko
3 2 0xffffffff829f3000 a540 opensolaris.ko
4 1 0xffffffff829fe000 7180 ums.ko
5 1 0xffffffff83019000 5954 cuse.ko
6 1 0xffffffff8301f000 b98 coretemp.ko
7 1 0xffffffff83020000 15d20 if_iwm.ko
8 1 0xffffffff83036000 fb241 iwm7265Dfw.ko
9 1 0xffffffff83132000 12045f iwm7265fw.ko
10 1 0xffffffff83253000 4260 ng_ubt.ko
11 6 0xffffffff83258000 9e30 netgraph.ko
12 2 0xffffffff83262000 91b8 ng_hci.ko
13 3 0xffffffff8326c000 9c0 ng_bluetooth.ko
14 1 0xffffffff8326d000 cad0 ng_l2cap.ko
15 1 0xffffffff8327a000 1ba00 ng_btsocket.ko
16 1 0xffffffff83296000 21c0 ng_socket.ko
17 1 0xffffffff83299000 88d8 tmpfs.ko
18 1 0xffffffff832a2000 acf mac_ntpd.ko
19 1 0xffffffff832a3000 12cab0 i915kms.ko
20 1 0xffffffff833d0000 763b0 drm.ko
21 4 0xffffffff83447000 10eb0 linuxkpi.ko
22 3 0xffffffff83458000 12f30 linuxkpi_gplv2.ko
23 2 0xffffffff8346b000 6d0 debugfs.ko
24 1 0xffffffff8346c000 18dc8 ext2fs.ko
25 1 0xffffffff83485000 fcf0 fusefs.ko
26 1 0xffffffff83495000 3d94 geom_linux_lvm.ko
27 1 0xffffffff83499000 a210 if_lagg.ko
Probably is the linuxkpi.ko driver that handles the brightness.
Anyway thank you again for the support, if I find some info I will post it here.
Ha! Thanks a lot. I have a Thinkpad T450s where changing screen brightness didn’t work either.
Without acpi_video.ko loaded it all works now.
Off topic: I want to mark this thread as solved. How can I do it ?
The necessary plugin to mark a thread solved was not yet installed. 
You can now select the post that solves a thread.
And it is now possible to add spoilers. 
We could conditionally load acpi_video(4) by our load_acpi script, depending on the system it is running on. What does kenv | egrep 'smbios.system.(maker|product|family)' show, @lme and @Maurizio?
On my laptop:
$ kenv | egrep 'smbios.system.(maker|product|family)'
smbios.system.family="ThinkPad T450"
smbios.system.maker="LENOVO"
smbios.system.product="20BUS06B00"
Thank you, the patch works for me.
fyi - disabling acpi_video.ko is also needed for lenovo thinkpad x230.
Fn-8 / Fn-9 are functioning now as expected …
best regards, _sg
Just today (january 2021) I solved a similar issue (read Brightness increment/decrement doesn't work in Lenovo Thinkpad x260).
Solution thanks to @mk1
# sysrc load_acpi_enable=NO
And reboot your laptop.