# "Fn" key not recognized to change the screen brightness on Dell laptop.



## Pardub (Mar 20, 2021)

Hi,

My laptop is a dell latitude 7240 with a Haswell cpu. 

Mate Desktop is installed.

My goal is to get the “fn” working to change the screen brightness.

I installed https://www.freshports.org/graphics/intel-backlight and I can change the screen brightness by entering ,for.e.g, “intel_backlight=40”.

It works as well by doing “ hw.acpi.video.lcd0.brightness=40”.

I followed the instructions in this post http://www.daemonology.net/blog/2020-05-22-my-new-FreeBSD-laptop-Dell-7390.html  where the author said:

_“I want to be able to control the brightness of the screen (aka. the backlight connected to the Intel video chipset):

# pkg install intel-backlight

and in particular to be able to control it via the function keys (Fn+Up, Fn+Down) which Dell exposes via ACPI:

# echo 'acpi_video_load="YES"' >> /boot/loader.conf

# cp /usr/local/share/examples/intel-backlight/acpi-video-intel-backlight.conf \

/usr/local/etc/devd/_ “

The keys associated for the screen brightness are the “Fn” and the top arrow to increase the brightness and the down arrow to decrease.

The problem is when I press the “fn” key with one of those keys, nothing happens but I can see the screen very slightly flashing but there is no light increased or decreased.

Please note the “fn” key is working fine if I want to change the keyboard backlight by pressing “fn” and the right arrow .


How can I use the “fn” key to modify the screen brightness ?


Thank you for your help.


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## Mjölnir (Mar 20, 2021)

I had to `sysrc kld_list+=" acpi_ibm"` for the screen brightness to be adjustable via the Fn keys on my ThinkPad laptop.  Unfortunately, there is no acpi_dell(4)...  Please consider to file in a bug report @Dell: _"Please publicly document the I/O ports & relevant ACPI interface stuff to enable open source OSs to access the Fn keys of your laptops"_. Hint: crawl the _Weltnetz_ for L*x stuff on Dell ACPI laptop stuff. Maybe they figured that out, and it can be ported to FreeBSD.


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## Pardub (Mar 20, 2021)

Thank you Mjölnir.
I tried to open a bug with Dell but apparently, this has to be done through a service request.
And when I logged to my Dell account, I got the following message:
_"Your product is out of warranty.
Service requests are not available for this product.Please use a different contact option"_
I contacted them through Tweeter.I don't have that much hope but let's see what will happen 
I spent a few hours looking for a solution and most of the time ,the possible answers came from the Arch forum.
I tried a few things  that could have been helped to sort this out like with showkey xbinkeys xmodmap xbacklight but it was unsuccessful ...
The link I posted in my previous let me think it was possible as the author ( Colin Percival) was able to use his "Fn" keys from a Dell laptop.
I keep searching and will post if I find something that could help.


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## Mjölnir (Mar 20, 2021)

Consider to also write an e-mail to the mailing list (you have to subscribe 1st) e.g. <freebsd-desktop> or contact <cp@> directly, maybe he can point you in the right direction.


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## Pardub (Mar 20, 2021)

Thank you for the insights,Mjölnir! I will do as you suggested.


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## aragats (Mar 25, 2021)

Mjölnir said:


> I had to `sysrc kld_list+=" acpi_ibm"` for the screen brightness to be adjustable via the Fn keys on my ThinkPad laptop.


Yesterday I set up FreeBSD 13 on a Lenovo IdeaPad. I had to use acpi_video instead.


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## Mjölnir (Mar 25, 2021)

They're changing the ACPI BIOS interface with every new model...  This whole PC stuff keeps scratching my nerves for decades now...   And that new ARM stuff is even worse, no standards @all...


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