Backlight fails frequently on boot with custom kernel
 

Hi, first post here. :)

I have been having issues with my netbook's backlight on a 3.0 kernel I have compiled. Every few boots, the screen will turn fullbright, as the kernel prints out:

Any attempts to change the brightness with the fn keys afterwards causes this to be printed out:

Rarely (I've only gotten this once) I can change the brightness afterwards, even though it still prints out the errors. When I look in /sys/class/backlight/ when the errors get thrown, it is completely empty, otherwise it has a folder named acpi_video0.

This happens both with a .config based on the (working) Arch Linux kernel I am running now, and with a "make defconfig" that I tweaked to include the drivers that I want. I'm a bit confused as to where to start looking for a solution since the majority of the time it does work properly. It's just the times when the screen gets forced to an eye-searing brightness that I have problems.

If anyone is able to help, I would be most appreciative. Thanks in advance. :)

I think more info might be needed, for example post the .config or the parts in the graphics section, and what brand of netbook is this ?

Sure, here's the kernel .config file, not sure exactly which parts to post so I'm just doing the whole thing: http://pastebin.com/c62bNz7j

Here's a paste of dmesg when it fails to get the backlight working: http://pastebin.com/2CcwLzKA

The netbook is an Acer Aspire One AO532h.

Maybe this will help
http://ubuntuforums.org/showthread.php?t=881241

Ialso noticed you have settings for dual-head not sure if it's relevant

I'd prefer to avoid hacks like that since the backlight works perfectly on Arch Linux supplied kernels.

You mean "ACPI: Video Device [OVGA] (multi-head: yes rom: no post: no)"? It's the same on the working kernel.

Oh, and I believe that I forgot to mention that the previous kernel I had compiled myself (2.6.35) had very similar issues. I can't say exactly since it was a while ago and I didn't pay too much attention to it.

Thanks for your time thus far. :)

Are you just compiling for the fun of it or for a specific reason?
Also the suggested info was not a hack if you read it it gives you control of the adjustments up & down, I elieve that you looked at the first option 50% not at the full configuration file, have you checked your settings.

See:
https://bugs.launchpad.net/ubuntu/+s...ux/+bug/428910

Try adding "acpi_backlight=vendor" to the append line in '/etc/lilo.conf', then run 'lilo' as root.

I am doing this just for "fun". I also wanted to set my CPU type to Intel Atom and take advantage of any optimization that did.

The backlight fix you linked to was, in fact, a hack. It was a workaround fix for something that sometimes works on this kernel, and that always works on Arch Linux supplied kernels. It addresses the symptoms, not the cause. Sorry, but that is no solution for me.

"acpi_backlight=vendor" does not help, I had tried it prior to posting here. If I recall correctly, it just made the backlight go fullbright 100% of boots. Furthermore, the launchpad link is old, and it does not accurately portray my problem.

Arch Linux's newly released Linux 3.0 does not have this issue.

I am now going to try compiling with this currently working config to see if I still run into problems. If I do, then I will look and see what patches Arch Linux might have applied and see if any of them fix it.

Thanks so far. :)

I have just compiled Linux 3.0.1 from source using an unmodified Arch Linux config. It does not appear to have the backlight issue.

At this point, I am confused as to what I did that broke it. It's not like there's an option in the setup named "Make backlight work on only some boots". :( Common sense says that the backlight would either work 100% or 0% of the time, depending on whether the driver was installed, right?

Here's the good config. http://pastebin.com/pYuDUpGH

You obviously used the old configuration file from original install.

I just did a apt upgrade on vbox & it worked well. I might try it on my wheezy hdd for my laptop, which was having network problems so I switched back to hdd with Squeeze on it.

Originally it was a bug in the kernel. I think they may have fixed it in the most recent release.

Yes, that was the point. I had wanted to see if the problem persisted if I used the same config as the working kernel. I'm not sure what you're trying to say here.

Not sure how that would be quite possible, since I've never had this issue on my netbook with Arch Linux kernels since I switched it to Linux (2.6.34).

When I get the time, I will try out a customized config again, and if the problem seems to be gone, I'll mark this as resolved.

I customized my 3.0.1 config, recompiled, and am no longer able to reproduce this issue.

Marking it as solved.

Nice to know that you have solved your issue, I recently upgraded from wheezy 2.6.38 to 3.0 on my laptop & am working thru my issues, laptop mode wasn't working also Gtk pixbuff, partially fixed, had to edit /usr/sbin/laptop_mode for unhandled kernel version errors. I have a few more issues but they'll soon be resolved. My virtual machine works fine though.

Congrats on your success!