XPS 13: cannot switch keyboard backlight back to automatic

[victorhqc]

The backlit keyboard works automatically when the ambient light changes, until I press the toggle button, then the behaviour becomes fixed (stops the automatic change of light)

[Kamal Mostafa (kamalmostafa)]

Confirmed. After pressing Fn-F6 key for the first time to manually select one of the 3 keyboard backlight brightness levels {full, medium, off} there does not seem to be any way to get back to "auto" mode (but pressing Fn-F6 continues to work to cycle through those three levels.

[Kyle Fazzari (kyrofa)]

This appears to be a hardware limitation: the keyboard appears to handle its own backlighting functionality. Can anyone confirm that this works the same way on Windows?

[Anders Østhus (aosthus)]

I've tested it on Windows 8, and if you put the backlight to either max or medium, it is still in the auto mode.
This is on the new HD version of the XPS 13, with the A08 BIOS.

[Kyle Fazzari (kyrofa)]

Anders I don't quite understand. In Ubuntu, after a reboot, the keyboard backlight is in automatic mode (it adjusts depending on ambiant brightness). Upon pressing Fn+F6 it goes to Medium for me, pressing it again makes it go Off, and pressing it again makes it go High. Pressing it again makes is go Medium, and it cycles through those three options in that order with no way to get it back to automatic. Can you describe what happens in that scenario in Windows, please?

Thank you!

[Anders Østhus (aosthus)]

I'm sorry, I mixed up the functions.

I've done some testing in Windows 8 today, and it doesn't seem like the ambient sensor is active at all actually. I'm reliably able to get the ambient sensor to work on initital boot in Ubuntu. In Windows 8, even if I hold it under a bright lamp, the keyboard backlight still turns on, even though in the same conditions (under a bright light in Ubuntu), the keyboard backlight stays off.

So to summarize, my findings so far is:
Ubuntu:
After initial boot, the ambient sensor works. After manually changing the backlight through the function keys, the ambient sensor does not work.
Windows 8:
Ambient sensor does not seem to work, or is requiring different light levels. Not really sure, I'll test more tomorrow.

[Bib (bybeu)]

Same behaviour in my L322X raring 3.8.0-31-generic x86_64 BIOS mode.
The thing is we do not have an OSD popup for F6 like the one we have for the LCD backlight

[Gabriele (questaemia)]

Same with the XPS13 9333.

The problem seems to be that the auto mode can be set only via software. Windows can do that through an application provided by Dell (backlitkb.exe, see the screenshot attached, it also allows to set the backlight timeout).

I find really annoying that this feature is available only for Windows users.

[Bib (bybeu)]

Maybe related to this: https://bugs.launchpad.net/linux-kernel-headers/+bug/1332425
Do you have this behaviour too?

[Gabriele (questaemia)]

With no driver to control the keyboard backlight, it will never change if not through the Fn keys.

I'm actually able to turn it on (max) and off (no auto and medium brightness) using smbios-token-ctl, but a proper WMI driver is what we need.