Bug 47286

Summary:	brightness changes on Samsung NF310 triggers permanent brightness fluctuations and system lock-up
Product:	libbacklight	Reporter:	Frank Schaefer <fschaefer.oss>
Component:	general	Assignee:	Matthew Garrett <mjg59>
Status:	NEW ---	QA Contact:
Severity:	critical
Priority:	high
Version:	unspecified
Hardware:	x86 (IA32)
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:

Description Frank Schaefer 2012-03-13 11:43:23 UTC

Changing the display brightness of the Samsung NF310 netbook triggers permanent brightness fluctuations. After a few seconds, the machine hangs up.
This makes the device unusable, because brightness changes are also caused by power management events.

Backlight adjustment of this machine seems to go through the "samsung-laptop" kernel module.

I did the following experiments:

1.) Changing the brightness with 
   echo "[1-8]" > /sys/class/backlight/samsung/brightness
and NO X-server running
=> works as expected (so it seems to be no kernel bug)

2.) Changing the brightness with 
   echo "[1-8]" > /sys/class/backlight/samsung/brightness
and X-server running
=> brightness changes to a random value. The system does NOT become unstable. After repeating the command two times (which also results in a random change) the right level is reached. Further repetitions of the command have no effect. 

3.) Changing the brightness with the xbacklight tool
=> triggers the instability

In case of 2.) and 3.) dmesg gets spammed with the following message:

"ACPI: Failed to switch the brightness"

I'm using openSUSE 12.1 with Xorg 7.6.

Comment 1 silberzin 2012-07-30 08:37:17 UTC

Hi All

I installed OpenSUSE on my Samnsung QX412 with processor 64. I have a brightens problem as below described. Imply is impossible for me to work on that laptop.
I can not adjust brightens. Screen start blinking and hang the PC.
If I work on battery system use a lot of battery and I have bad performance.

I think I could adjust brightens right after system installation from DVD, but after updates (i installed all updates at once) I got the problem.

Can you please help with that?

Than you.

BR
Rafal

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