On my new Dell E7470, the keyboard backlight driver doesn't seem to work correctly. I can contral the backlight using the keyboard (Fn+F10), but the /sys interface seems to be malfunctioning: The dell_laptop driver does provide entries in /sys (in /sys/devices/platform/dell-laptop/leds/dell::kbd_backlight). Reading from the "brighness" entry there works fine (and the entry returned corresponds with reality), but writing to "brightness" has no, or incorrect effects: ╰─▶ cat brightness 0 ╰─▶ echo -n 1 > brightness ╰─▶ cat brightness 2 ╰─▶ echo 0 > brightness ╰─▶ cat brightness 2 ╰─▶ echo -n 0 > brightness ╰─▶ cat brightness 2 In addition, there is a warning (error?) in dmesg for each write to "brightness": [26628.114977] dell_laptop: Setting old previous keyboard state failed
Oh, and for completeness sake: ╭╴root@regan:dell-laptop/leds/dell::kbd_backlight ╰─▶ ls -la total 0 drwxr-xr-x 3 root root 0 jan 1 21:24 ./ drwxr-xr-x 3 root root 0 jan 1 21:24 ../ -rw-r--r-- 1 root root 4,0K jan 2 15:39 brightness lrwxrwxrwx 1 root root 0 jan 2 15:41 device -> ../../../dell-laptop/ -r--r--r-- 1 root root 4,0K jan 2 11:38 max_brightness drwxr-xr-x 2 root root 0 jan 2 15:33 power/ -rw-r--r-- 1 root root 4,0K jan 2 15:33 start_triggers -rw-r--r-- 1 root root 4,0K jan 2 15:33 stop_timeout lrwxrwxrwx 1 root root 0 jan 2 11:02 subsystem -> ../../../../../class/leds/ -rw-r--r-- 1 root root 4,0K jan 2 15:33 trigger -rw-r--r-- 1 root root 4,0K jan 1 21:24 uevent ╭╴root@regan:dell-laptop/leds/dell::kbd_backlight ╰─▶ cat max_brightness 2
https://bugzilla.redhat.com/show_bug.cgi?id=1436686 leds dell::kbd_backlight: Setting an LED's brightness failed (-6) on Dell Precision 7510/0M91XC and 4.10.5-200 [ 5.536399] dell_laptop: Setting old previous keyboard state failed [ 5.536434] leds dell::kbd_backlight: Setting an LED's brightness failed (-6) [ 16.228184] dell_laptop: Setting old previous keyboard state failed [ 16.228189] leds dell::kbd_backlight: Setting an LED's brightness failed (-6) [ 519.918079] dell_laptop: Setting old previous keyboard state failed [ 519.918085] leds dell::kbd_backlight: Setting an LED's brightness failed (-6) [ 549.868267] dell_laptop: Setting old previous keyboard state failed [ 549.868271] leds dell::kbd_backlight: Setting an LED's brightness failed (-6)
https://github.com/torvalds/linux/pull/407
This will be fixed in https://patchwork.kernel.org/patch/9695271/
This has now been fixed in master: https://github.com/torvalds/linux/commit/9216e0dcb5533a999d544d0af8661118e0588e1d