+1, Dell Latitude E7470. 

Preinstalled Dell's Ubuntu 14.04.X does not seem to have this problem, if I remember it right.

Fedora 26 actual (Kernel 4.11.0-0.rc3) is also affected. Logs are the same.

Sorry for making so much noise but I uncovered some more details (F26, K4.11.0-0.rc3).

Keyboard backlight still could not be controlled from Gnome Settings, but if you turn off the light with Fn+F10 and wait for the laptop to go to sleep it will turn keyboard backlight back ON while turning the screen off.

There was exactly one commit to drivers/platform/x86/dell-laptop.c between 4.9 and 4.10

commit 1d161d4cd719ac498545c94805803af8af9b642f
Author: Hans de Goede <hdegoede>
Date:   Wed Oct 26 17:17:44 2016 +0200

    platform/x86: dell-laptop: Use brightness_set_blocking for kbd_led_level_set
    
    kbd_led_level_set uses dell_smbios call which blocks, so the kbd_led
    classdev should use the brightness_set_blocking callback.
    
    Signed-off-by: Hans de Goede <hdegoede>
    Reviewed-by: Pali Rohár <pali.rohar>
    Signed-off-by: Darren Hart <dvhart.com>

Which seems like a good candidate for causing problems. Hans, any idea?

Hi,

(In reply to Laura Abbott from comment #4)
> There was exactly one commit to drivers/platform/x86/dell-laptop.c between
> 4.9 and 4.10
> 
> commit 1d161d4cd719ac498545c94805803af8af9b642f
> Author: Hans de Goede <hdegoede>
> Date:   Wed Oct 26 17:17:44 2016 +0200
> 
>     platform/x86: dell-laptop: Use brightness_set_blocking for
> kbd_led_level_set
>     
>     kbd_led_level_set uses dell_smbios call which blocks, so the kbd_led
>     classdev should use the brightness_set_blocking callback.
>     
>     Signed-off-by: Hans de Goede <hdegoede>
>     Reviewed-by: Pali Rohár <pali.rohar>
>     Signed-off-by: Darren Hart <dvhart.com>
> 
> Which seems like a good candidate for causing problems. Hans, any idea?

All that that commit does from this bug's pov is that it now propagates errors (and the LED core now reports them). As per the description of the bug: 

"In 4.8 and 4.9 kernels no such messages appeared and Dell keyboard backlight could not be software controlled.

The backlight still cannot be software-controlled in 4.10 but now these messages appear"

Things were already not working in 4.8 / 4.9, my commit just causes an error to actually get logged for this now :)

Error -6 is -ENXIO which comes from dell_smbios_error() which says: 

        case -2: /* Function not supported */
                return -ENXIO;

So the dell-laptop code definitely doing something wrong, but what exactly that is the question.

Thanks for clarifying. The best way to get this fixed would be to report it to the x86 platform maintainers, ideally via an e-mail to the list but I think they check the kernel.org bugzilla as well.

That's the upstream bug report: https://bugzilla.kernel.org/show_bug.cgi?id=191731

Some additional reading material:
https://github.com/dell/libsmbios/issues/17
https://www.spinics.net/lists/platform-driver-x86/msg11195.html

Time permitting I'll be fixing dell-laptop module to fix the keyboard LEDs. I'll keep everyone posted on the progress.

https://github.com/torvalds/linux/pull/407

This patch supersedes mine: https://patchwork.kernel.org/patch/9695271/

The patch is now in main: https://github.com/torvalds/linux/commit/9216e0dcb5533a999d544d0af8661118e0588e1d

Please backport into F25/F26 train.

sounds like it's fixed.

is the patch coming to f25?

kernel-4.10.15-200.fc25 has been submitted as an update to Fedora 25. https://bodhi.fedoraproject.org/updates/FEDORA-2017-4537a2fbdc

kernel-4.10.15-100.fc24 has been submitted as an update to Fedora 24. https://bodhi.fedoraproject.org/updates/FEDORA-2017-9a479a2cff

kernel-4.10.15-200.fc25 has been pushed to the Fedora 25 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-4537a2fbdc

kernel-4.10.15-100.fc24 has been pushed to the Fedora 24 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-9a479a2cff

I can confirm that kernel-4.10.15-200.fc25 is working with Dell Precision 7510/0M91XC, that keyboard brightness can now be regulated with KDE Plasma widget and in response to power events.

kernel-4.10.15-200.fc25 has been pushed to the Fedora 25 stable repository. If problems still persist, please make note of it in this bug report.

kernel-4.10.15-100.fc24 has been pushed to the Fedora 24 stable repository. If problems still persist, please make note of it in this bug report.

Will this be applied to F26?

Yes, F26 seems to have gotten lost in the shuffle. We're still in beta freeze so once that ends the patch can be applied there too.

Can the fix be applied to F26 now?

The error is back on 4.15.4-300.fc27.x86_64. This is a regression from 4.15.3.fc27.

[    5.614704] dell_laptop: Setting old previous keyboard state failed
[    5.614725] leds dell::kbd_backlight: Setting an LED's brightness failed (-6)

I have the same problem on a Dell Precision M4800 with the latest Fedora 27 kernels. The keyboard backlight is never working correctly, when the laptop boots it gets switched off completely, if I reactivate it with the Fn keys it lights up only for 1-2 seconds at every keyboard tap which makes it pretty unusable. Also, I noticed that every time I boot in Fedora, the BIOS settings got reset to 25% illumination level, while I set them at 75%, clearly recent Fedora kernels mess
up with the backlight and the BIOS.
I have also a Latitude E7270, where the problem is less serious, still Fedora when booting switches off the keyboard backlight, but with the Fn+F10 keys I can get it working properly again.
All this with kernel-4.15.6.fc27, x86_64

Regression is gone on 4.15.7-300.fc27.