Arch Linux

Britzel

Member

Registered: 2010-10-17

Posts: 4

Samsung N510 Backlight issue

Hi,
I know that this topic has been beaten to death in the forum and the wiki, still I don't arrive at getting it to work. Although I am close. I think...

Hardware
Samsung N510, older 2009 model with AR5001 wlan chip, 2GB RAM, 160GB disc, Atom N270, Nvidia MCP79 Chipset with C79 [Quadro FX 470M] Ion graphics

SW
Archlinux
kernel: 2.6.35-ARCH
Gnome 2.32.0-1
xorg 1.9.0-1
xf86-video-nouveau 0.0.16_git20100819-1
nouveau-dri 7.8.2-3
pm-utils 1.4.0-1

daemons from rc.conf

DAEMONS=(syslog-ng dbus hal network wicd ntpd netfs laptop-mode crond alsa)

modules from rc.conf

MODULES=(acpi-cpufreq)

All other modules are loaded by udev (incl. acpid, it's running).

What works:
- Keycodes from Fn+Up (225) and Fn+Dn (224) are recognized, as well as all other special keys. I assume that's thanks to udev reconizing the right keyboard and loading the samsung-other keymap. I didn't touch udev confs. showkeys works nicely and displays the keycodes.

- brightness in /proc is present:

gin ~ # cat /proc/acpi/video/IGPU/LCD0/brightness 
levels:  20 30 40 50 60 70 80 100
current: 40

- manually setting the brightness works

$ echo 100 > /proc/acpi/video/IGPU/LCD0/brightness

results in full brightness

- brightness in /sys is present and changes when pressing Fn+Up/Fn+Dn

gin ~ # cat /sys/class/backlight/nv_backlight/brightness 
1025

1025 is the max value here.

- Fn+Up/Fn+Dn work when still in grub-menu

- When using the Fn+Up/Dn keys Gnome shows a small brightness indicator with a horizontal bar which changes apropiately, similiar to volume control.

What does not work?
- Gnome Power Management settings relevant to backlight brightness
- Gnome power manager LCD brightness applet
- xbacklight says 'No outputs have backlight property'.

What did I try so far?
- Arch forum & wiki. Followed several HowTos etc. All to no avail.
-- xmodmap setting is not required since the keycodes are properly reconized. Tried it anyway, no help.
-- poking hexvalues into the PCI system, as suggested in the wiki and some other fora (fedora, gentoo etc). This does not work a) because the VGA card has a different bus identifier, the wiki suggest 00:02.0, my vga card sits on 02:00.0; b) I tried it anyway with horrendous results, screen going really funny. Finally I stopped poking random hex values before I brick my netbook :-)
-- adding 'acpi_backlight=vendor' to kernel line in grub menu. This results in the /proc entry not working anymore (it's still present though).
-- Changing BIOS setting for backlight keys from 'auto' to 'user' and back. No difference seen.
- googled for xbacklight and 'No outputs...' message. Got a lot of results, bug reports etc. All led back to the suggestions already mentioned, no help.
- Installed custom keyboard shortcuts for Fn+Up/Dn which I could map to a bash/perl script if I wanted. But that doesn't seem right... see below.
- configured laptop-mode confs, telling it to use /proc/acpi/video... and use "echo <value>".  Used different brightness setting for AC/Bat modes, but no change when plugging in/out the AC adaptor. The pm-utils recognize that change though, the icon in the panel changes.

Conclusion so far
Input works, keycodes are recognized
Low level output works (echo n > /proc...)

So what's missing? Some part which maps the key events to the /proc or other system. Writing my own helper script is possible, but I have the feeling that I am just missing a small part. Which?

TIA,
Britzel