[Pkg-xfce-devel] Bug#773913: Bug#773913: Bug#773913: Lightdm switches immediately to a black screen

Yves-Alexis Perez corsac at debian.org
Mon Mar 30 08:22:09 UTC 2015

Hash: SHA512

On Mon, Mar 30, 2015 at 12:18:20AM +0200, Thomas Goirand wrote:
> Hi Yves-Alexis,
> I have experienced the same issue as described by Fabien.
> What happens is, if I leave my laptop unused for a (very) long period of
> time idle, it goes into darkness (slowly fades out, then full screen black).

So something in your desktop environment handles the brightness and sets
it to minimum?

> When I want to wake-up my latop, I just press any key. This wakes up the
> laptop, but it does *not* set the screen brightness back to normal.

> Increasing the brightness on the lightdm password prompt doesn't work.

I assume your laptop needs something in userspace to handle the
brightness keys, then?

> However, if I just type my password (blankly, hoping it works...), then I
> get to X (using the mate Desktop in my case), then brightness control works,
> and I can see the screen again.

Because MATE handles the brightness keys.
> Before I knew this trick, I thought my laptop was crashed. So I just powered
> off, then on again. But then when lightdm gets back, it sets the brightness
> to zero again (meaning screen is off in my case), and I can see nothing. The
> only way is again, to type my login and password blanking (without any
> control to see if I typed correctly), then when X start, I can set the
> brightness again.
> I can confirm that the issue is in lightdm, because gdm doesn't have this
> issue. I'm also using systemd. I'm using the Nouveau driver (and probably
> also the intel i915 since my laptop has 2 cards). I'm not sure this is
> related to video board and driver, but I thought it was a good info.

It's somehow related yeah. Brightness keys handling has been a mess
these past years. It was once handled completely by the laptops embedded
controller, then it was done by the kernel/ACPI, then by the driver,
then by basically noone (since Windows 8 laptops), so it has to be done
in userspace.
> I believe that the best way to fix it, is to make sure that the brightness
> controls are *always* working in lightdm. If I get back to lightdm with a
> black screen, I don't really mind if I can fix that by increasing the
> brightness...

Sure, but I'm not sure handling the brightness keys are really the role
of a login screen. I'll forward this upstream but don't hold your
> If I may help to debug the issue in any way, let me know. I'd be happy to do
> whatever you propose to debug the issue or test some fixes.

It might help to know which kind of laptop it is.

- -- 
Version: GnuPG v2


More information about the Pkg-xfce-devel mailing list