Arch Linux

The_Major

Member

From: Newport, UK

Registered: 2008-03-31

Posts: 18

Kernel upgrade results in dimming issue.

I just carried out an upgrade and got kernel 2.6.25, however whenever I reboot my laptop my lcd backlight dims about halfway through the boot process, luckily I can increase the brightness on my laptop using the function keys, but its really annoying.

The dimming only manifested itself after the upgrade and I have trawled through /sys/devices and /sys/class looking for the persistent setting, I think I have narrowed it down to /sys/class/backlight/acpi_video1/brightness but I whatever setting I use gets lost on reboot and reverts to 0 (this seems to be about 45% brightness and 10 appears to be 100%)

Has anyone got any ideas how I can fix this?

Thanks in advance

Mark

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hagbard

Member

Registered: 2008-01-21

Posts: 2

Re: Kernel upgrade results in dimming issue.

This is happening to me too. It dims when the ACPI loads during the boot process.

-Anthony

The_Major

Member

From: Newport, UK

Registered: 2008-03-31

Posts: 18

Re: Kernel upgrade results in dimming issue.

It appears to  happen to me when udev is loading, my udev rules changed when the kernel updated (50-udev.default.rules) but I cant see anything in there that would effect the screen!!

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sph

Member

Registered: 2008-05-01

Posts: 63

Website

Re: Kernel upgrade results in dimming issue.

Quick and dirty workaround.

Add the following line to your /etc/rc.local:

echo 4 > /sys/class/backlight/acpi_video0/brightness

Open a terminal and type the following to see the max. brightness value:

cat /sys/class/backlight/acpi_video0/max_brightness

To see the actual brightness value:

cat /sys/class/backlight/acpi_video0/actual_brightness

Last edited by sph (2008-05-28 18:34:00)

The_Major

Member

From: Newport, UK

Registered: 2008-03-31

Posts: 18

Re: Kernel upgrade results in dimming issue.

Thanks SPH, I had thought of that (my lcd is actually acpi_video1 for some reason) but I have been having other issues with the 25 kernel so I have downgraded to .24 for now.

Cheers for all your help.

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schimpfj

Member

From: Frankfurt, Germany

Registered: 2007-08-15

Posts: 53

Re: Kernel upgrade results in dimming issue.

Thank you SPH for pointing me to this thread from my initial one and for your work around. Works fine for me, but I also picked acpi_video1.

cb474

Member

Registered: 2009-04-04

Posts: 469

Re: Kernel upgrade results in dimming issue.

I'm having a similar issue. I think it occurred after the upgrade to 2.6.29. On boot my brightness gets reset to a very low level. This is the case as soon as the grub menu appears. The bightness remains dim through the startup process. Then when I login to Gnome, the brightness readjusts itself to the highest level. Any thoughts what's going on here? Still a kernel bug? Is adding the command (above) to /etc/rc.local still the only solution?

Perhaps as a related issued, I just realized that the backlight goes completely off when the computer is shutting down. I thought the dmesg just had stopped displaying during shutdown for some reason. But I now realize that the backlight is off. [Edit: actually now I see that the backlight goes off for a second, then comes on but the screen is blanked, and then goes off again when the laptop powers off (of course). So maybe this isn't related to the dim screen at startup.]

Last edited by cb474 (2009-04-13 21:06:06)

cb474

Member

Registered: 2009-04-04

Posts: 469

Re: Kernel upgrade results in dimming issue.

I discovered my version of the dimming on reboot problem is associate with gdm. I was using slim instead to troubleshoot a different problem and with slim the screen was no longer dimmed on reboot. But when I went back to gdm the problem returned. I wonder why Arch is using gdm 2.20, when the latest stable version from gnome is 2.24? (See: http://projects.gnome.org/gdm/) Although I see gnome has recently updated 2.20 as well. It's like there are two different versions being developed.

cb474

Member

Registered: 2009-04-04

Posts: 469

Re: Kernel upgrade results in dimming issue.

I found this problem is solved when I swithced from launching GDM as a daemon with rc.conf and used inittab instead. See: http://wiki.archlinux.org/index.php/GDM

Leye

Member

From: Heidelberg, Germany

Registered: 2008-09-03

Posts: 96

Re: Kernel upgrade results in dimming issue.

Hi,

I have a similiar problem: Whenever X starts, regardless of "plain" X or GDM/GNOME, and also when udev starts during boot, my display becomes darker. If I kill a GNOME-session, and GDM starts up, the screen dims again. Since it also gets dark during udev, I wonder if there's another reason for that ...