So, I decided to install Slackware on my lappy to coexist with my Arch installation but I've found that the brightness controls are not working. Furthermore looking at /sys/class/backlight lists no other folders.

I've tried a variety of kernel parameters such as acpi_backlight=vendor acpi_osi=, acpi_osi='!Windows 2012' etc and none of them fix this. To get it working under arch, I just needed acpi_backlight=vendor - however it is running a newer kernel but I'm not sure if that matters all too much. The intel drivers are installed and appear to be loaded as well as the toshiba_acpi module for the laptop.

Aside from trying a newer kernel, are there other things I should look into?

Laptop model: Toshiba C50-B032
Slackware version: 14.1
Kernel 3.10.17 - generic smp (also occurs with huge smp)
Bootloader: Grub, configured through Arch

I also updated and installed/upgraded new packages, but aside from that it's a stock install.

it might help if you add some more info, for example the laptop model.

Yes of course, sorry forgot to add that. I'll update the initial post.

Bump - Any more details I can add?

adding these kernel params got it working for me, in KDE anyway:

# Append any additional kernel parameters:
append=" vt.default_utf8=0 acpi_osi=\"!Windows 2012\" acpi_osi=linux "

Are you using KDE? or maybe you just need to bind the control to the fn key in whatever desktop you are running? (i.e. maybe it is all ready to work, but no button tied to the brightness control?)

I got that working by appending acpi_backlight=vendor acpi_osi=!Windows 2012 in LILO but after some days I was thrown back to no fn keys working situation on my Thinkpad L412. I shut down the laptop, removed the battery and pressed the power button and kept pressed for 10 seconds(returning to factory defaults in BIOS).
That worked and still has been working good, don't ask me how.

Regards.

Thanks guys, I will give those options a go tonight when I have Slackware back on and let you know. I had to reinstall everything on my lappy and have yet to get everything back in order.

EDIT: I forgot to add I am using KDE, but xfce was no better.

Do you see any listings under /sys/class/backlight when running Arch installation? Which kernel is it using?

Yes, the folder is intel_backlight which lists information like current brightness and max brightness levels. Also, the current kernel on Arch is 3.15.8.