Fix for Toshiba laptops with no control of brightness after suspend

[marko]

I have a Toshiba Satellite R945 which always had nonworking display brightness control after the first time I wake the laptop from suspend to ram.

I then found this bug thread:
https://bugzilla.kernel.org/show_bug.cgi?id=21012


The workaround in post 19 worked great for me:

- add acpi_backlight=vendor in the kernel command line
- place the quoted 99toshiba script (below) in /etc/pm/sleep.d/ where the content of the script for /etc/pm/sleep.d/99toshiba is:

#!/usr/bin/env sh
# /etc/pm/sleep.d/99toshiba

if [ $1 == suspend ]
then
cat /sys/class/backlight/intel_backlight/brightness > /var/run/brightness
elif [ $1 == resume ]
then
echo 3 > /sys/class/backlight/toshiba/brightness
cat /var/run/brightness > /sys/class/backlight/intel_backlight/brightness
fi

Also remember to make it runnable to root:

chmod 744 /etc/pm/sleep.d/99toshiba

For those new to changing the kernel entries, just edit /etc/default/grub so that you add
"acpi_backlight=vendor" (no quotes) to the string named "GRUB_CMDLINE_LINUX" and run:

grub2-mkconfig -o /boot/grub2/grub.cfg

You can 'dryrun' that by just running:

grub2-mkconfig

this will display the whole contents of the future grub2.cfg to the console. You can filter out the irrelevent stuff by:

grub2-mkconfig 2> /dev/null | grep vendor | head -1

this will (or should) show one copy of the kernel command line and you can confirm your acpi_backlight=vendor is in there.
Now that you can see it would be properly put in, run it for real to change the on-disk grub.cfg:

grub2-mkconfig -o /boot/grub2/grub.cfg

at the next reboot, the backlight control should work even after wakeup from suspend to ram.
Note I've only had my problem with KDE so I don't know if Gnome or others has this problem with the backlight.