Kernel upgrade 3.15.3 -> 3.16.1 screen dimming broke

chias

I use XFCE, and I just updated my kernel from 3.15.3 to 3.16.1. Since updating, the screen dimming / brightening keys no longer dim the screen, which stays at full brightness (although the notice thing works, and indicates that the screen is dimming even though it isn't). The only effect the buttons do have is that when brightness gets to zero, the screen switches off entirely (which did *not* happen under 3.15.3).

The only way I've found of actually changing screen brightness is to unplug the laptop, at which point it dims to 20% brightness, but plugging it back in restores it to 100%. Booting into the 3.15.3 kernel makes the problem go away and dimming/brightening works as expected.

I configured 3.16.1 by simply copying my 3.15.3 .config file over and running "make menuconfig". Has anyone else seen this / know how to go about diagnosing what's wrong and fixing it?

Sulman · n00b Joined: 15 Feb 2014 Posts: 63

What's the hardware platform? Which gpu driver? I've found screen brightness hotkeys to be the one thing that periodically break whatever flavour of Linux you use.

It sounds like XFCE is recognising the keystrokes correctly but they're not driving anything anymore. Do you know what they map to? Perhaps that behaviour has changed, either in ACPI or for e.g. xbacklight.

chias · Posted: Sat Sep 20, 2014 10:10 am Post subject:

Thanks for the tips

Hardware platform is a "Samsung ATIV book 6", and I believe I'm using the Intel graphics drivers although the laptop does also have a Radeon card.

Since this issue arose both xfce4-power-manager and the kernel have both received an upgrade, and the problem remains

I don't know what the keys map to (I have not changed any keymappings from the defaults) and I don't have xbacklight installed.

EDIT: after installing xbacklight, I can now dim the screen by using xbacklight. The brightness keys continue to display the brightness changing notification without changing the brightness, though

albright · Posted: Sat Sep 20, 2014 12:09 pm Post subject:

Did you try the kernel boot parameter:

chias · Posted: Sat Sep 20, 2014 9:33 pm Post subject:

Correction to my previous post: xbacklight works with the old kernel only.

Thanks for the tip about the kernel boot parameter! I just tried it though, and screen dimming still does not work. My boot parameters are:

chias · Posted: Tue Sep 23, 2014 10:09 pm Post subject:

So this is interesting. I had a look in '/sys/class/backlight/intel_backlight':

albright · Posted: Wed Sep 24, 2014 11:39 am Post subject:

I'm curious if you boot from another linux distro cd or usb stick, do
the backlight keys work?
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chias · Posted: Wed Sep 24, 2014 10:52 pm Post subject:

Good question! Just booted using an Xubuntu live-usb, and yes the brightness keys work perfectly.

chias · Posted: Sun Oct 05, 2014 4:54 pm Post subject:

Because 100% and 1% are both fairly unusable, my current workaround is to use kernel 3.15.3 and use xbacklight to adjust the screen brightness. I'd really like to be able to update though... does anyone have any other ideas what might solve things?

chias · Posted: Tue Nov 11, 2014 8:04 pm Post subject:

I still haven't managed to make any headway on this... does anyone have any other suggestions?

Sakaki · Guru Joined: 21 May 2014 Posts: 409

Hi chias,

It may be that you are affected by this i915 issue?
If so, you might try setting:

chias · Posted: Sat Nov 22, 2014 3:11 am Post subject:

Hm, that didn't seem to help either.

Further investigation though shows that this issue continues to vex me even with a fresh Debian install on the same hardware. Which says to me that it probably isn't an issue to be fixed on the Gentoo forums :<