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-   -   Complete hang in 285.03 when changing brightness on NVS 4200M (http://www.nvnews.net/vbulletin/showthread.php?t=166387)

spanommers 09-17-11 04:37 AM

Complete hang in 285.03 when changing brightness on NVS 4200M
 
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My Lenovo T420 has an NVS 4200M. In my BIOS I have Optimus disabled and it is set to use discrete graphics. After configuring xorg.conf, X loads up and I can use the computer reasonably well. However, changing the brightness consistently hangs (e.g., using brightness keys on laptop, idle dimming in gnome-power-preferences). The machine is totally unresponsive: VT switching doesn't work, Magic-SysRq doesn't respond, and pressing caps lock does not toggle the keyboard light. It seems like the kernel is locking up.

I've found some other situations that render my computer unresponsive, but they're not always as reproducible.

I am running Linux Mint Debian Edition which follows Debian testing. I have reproduced this on 285.03 (packages from experimental) and 275.09 (testing).

I am currently using TwinView with an external monitor, but it is reproducible with no external displays connected.

I saw another user in a different forum apparently having the same issue: http://forums.nvidia.com/index.php?showtopic=207660

spanommers 09-17-11 06:34 PM

Re: Complete hang in 285.03 when changing brightness on NVS 4200M
 
I found that passing pci=noacpi as a boot parameter works around this issue for me. However it seems I cannot control brightness under X.

This might be a kernel bug and not an nvidia driver bug, because I later found that I could reproduce this from a virtual console without X running or the nvidia kernel module loaded.

vilgefortz 10-08-11 02:19 PM

Re: Complete hang in 285.03 when changing brightness on NVS 4200M
 
It does not hang with 3.0+ kernel. However, it does not work either in X. However, I noticed that hot keys actions are applied internally but no change happens until suspend/resume from RAM :)

So, with my current 3.1-rc9 kernel, the following works:
echo N > /sys/class/backlight/acpi_video0/brightnes
pm-suspend
[resume]

brightness is changed.


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