handling of brightness/backlight in the display manager

[Yves-Alexis Perez]

Hi,

I got a report from a Debian LightDM user which has issues with brightness keys in conjuction with LightDM.

I'm not completely sure of his setup, but I can think of a way to reproduce his problem:

- In this setup, the brightness is switched off after some idle time by the desktop environment
- The laptop is a post-Windows 8 laptop, where the brightness keys have to be handled by userspace
- Then (presumably using light-locker) the screen is locked and vt is switched to LightDM.

At that point, the display is off and the screen is locked, but pressing the brightness keys won't work because nothing receives the brightness keys event on that vt. Same thing happens at boot, where it's not possible to set the brightness in LightDM, actually.

The solution would be to handle those brightness keys in LightDM. I'm not a huge fan of this solution, and really prefered when the kernel was doing it, but kernels maintainers disagree with me on this, so eh…

Please note that I'm reporting against lightdm itself but maybe that's a job for the greeters. In that case it might still make sense to do that in the libs, since every greeter would need to do it.

[Yves-Alexis Perez (corsac)]

Some references:

https://bugzilla.kernel.org/show_bug.cgi?id=51231
https://bugzilla.kernel.org/show_bug.cgi?id=81691