Friday, November 18, 2011

Fedora 16 : LCD screen backlight brightness on Acer Aspire 5742 issue

Tonight I found a temporary solution on my Acer Aspire 5742 (thanks to GusCarracedo for
the clue) how to change a backlight brightness of my screen.
# ls -R /sys/class/backlight/
/sys/class/backlight/:
acpi_video0 intel_backlight

so...
# cat /sys/class/backlight/intel_backlight/brightness
976
<- This was an original value I found

# cat /sys/class/backlight/intel_backlight/max_brightness
976

# echo "400" > /sys/class/backlight/intel_backlight/brightness
...works perfectly fine, as a temporary solution of course.

Changing acpi_video0/brightness had no effect.

Please check this out as well:
https://launchpad.net/~kamalmostafa/+archive/linux-kamal-mjgbacklight
It is for i915 chip (found also in Aspire 5742).
I have intel_backlight interface, but it looks gnome-power-manager is not updated, so I am investigating this now.

I hope this will help Fedora developers to fix this issue permanently once and
for all.



---------------------------------------------------
Dmitriy Kalmykov suggested how to fix the issue (bug 753012and it seems to work also on my Acer Aspire 5742, so I would say it is worth to try and big thanks to Dmitriy :)

Open '/boot/grub2/grub.cfg' for editing.
Ignore the line '# DO NOT EDIT THIS FILE'.
Find the proper bootline which boots your kernel and add
'acpi_backlight=vendor' parameter in kernel options.

The part of my '/boot/grub2/grub.cfg' edited looks like that:

menuentry 'Fedora (3.1.1-2.fc16.x86_64)' --class fedora --class gnu-linux
--class gnu --class os {
 load_video
 set gfxpayload=keep
 insmod gzio
 insmod part_msdos
 insmod ext2
 set root='(hd0,msdos1)'
 search --no-floppy --fs-uuid --set=root 8cb738a0-95f4-4fe7-9c42-7d95aa3cc8da
 echo 'Loading Fedora (3.1.1-2.fc16.x86_64)'
 linux /vmlinuz-3.1.1-2.fc16.x86_64
root=UUID=76b94cf5-3dad-4b63-899e-2c99849fdde3 ro LANG=ru_RU.UTF-8 rd.md=0
rd.lvm=0 rd.dm=0 quiet rhgb rd.luks=0  KEYTABLE=us acpi_backlight=vendor
 echo 'Loading initial ramdisk ...'
 initrd /initramfs-3.1.1-2.fc16.x86_64.img
}