# ATTENTION! kernels 2.6.32/33 have KMS corrupted

## yendy

After upgrading kernel to 2.6.32-r7 (from 2.6.31-r6) when pressing key combination that controls screen brightness in my laptop the screen reacts by go blank. (And it remains so until reboot.) This happens only under xorg and not on the text console. 

When rebooted to the previous kernel version (2.6.31-r6) exactly the same system behaves flawlessly. So clearly the problem is in the newest version of the kernel. What to do?Last edited by yendy on Sat Apr 24, 2010 4:50 pm; edited 4 times in total

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## Rexilion

Looks like a kernel regression. I suggest you test the latest vanilla and see if the problem persists. If it does, you probably need to do a git bisect and report a bug to the kernel bugzilla.

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## yendy

What does "to do a git bisect" mean?

I've tried "~x86" the newest version, 2.6.33-gentoo-r1, and I confirm - the problem persists. 

In few minutes I will try out the newest vanilla, i.e. Latest Stable Kernel 2.6.33.2 downloaded from http://kernel.org

But I have a doubt... Maybe is there one of the features newly introduced in the version in question responsible? How to check it out? I took .config from the previous version and did 'make oldconfig' and answered all questions as "No". But it didn't help. Besides, there is one new feature impossible to switch off - 

General Setup ->  RCU Subsystem

and whats more the meaning of it is sth I can't understand, what is it? How to disable it?

EDIT:

I confirm, the problem persists in the latest vanilla  :Sad: 

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## Rexilion

The fact that a kernel option appears does not always indicate that something is 'new'. The option is now selectable (sometimes you can select between multiple).

With git bisect, you grab the source code and then 'travel in time' (reversing and re-adding changes of code) to find which change of code broke your brightness controls.

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## yendy

Now I observed this was not just about 'brightness control' but other controls too - namely these ones that evoke informative pop windows of the value they control. This feature (which worked in windows neatly) conflicted with linux anyway so far. But so far the discordance was such, instead of expected graphical representation of parameter being just tuned (like in windows) in linux it was unintelligible square on the screen popped up (exactly of the size and position of expected pop up window). It was ugly but bearable and whats important it allowed to work with this laptop without any interruption. But now when I touch any control that "should" evoke pop up info - then the screen goes blank. 

Why did these pop-ups that displayed well under windows conflict with linux previously? To understand it is probably the answer why this failed xserver completely now, in the newest kernel version...

EDIT:  now as I've checked the problem occurs only when KMS is activated (in  previous kernel's versions KMS worked not broken by laptop's info pop-ups)

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## yendy

So, I've tested the following kernels:

gentoo-sources-2.6.31-r6 -- worked good

gentoo-sources-2.6.31-r10 -- very well

gentoo-sources-2.6.32-r7 -- screen blanks on control pop-ups

gentoo-sources-2.6.32-r6 -- screen blanks even already during boot - when console comes into framebuffer mode

gentoo-sources-2.6.33-r1 -- screen blanks on control pop-ups

vanilla-sources-2.6.33.2    -- screen blanks on control pop-ups

vanilla-sources-2.6.34_rc5 -- works well!! (but there is no phc-intel for this version yet  :Sad: )

git-sources-2.6.34-rc5-git4 -- also works very well (but I can't apply phc-intel - does anybody know how?)

To sum up, the kernels 2.6.32 - 2.6.33 seem corrupted!,

but from 2.6.34 it looks like the community alleviated this (it'd be nice to know what exactly the issue was about?)

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