Created attachment 128037 [details] xorg.0.0log Running xorg on a Lenovo X1 carbon gen4 (skylake) with any recent Linux kernel (currently 4.8.8-1-ARCH), the backlight information vanishes after some time: Calling "xbacklight" gives an empty result: [10:56] feder:~% xbacklight [10:56] feder:~% xbacklight -set 100 [10:56] feder:~% echo $? 0 However when restarting xorg, it works for some time (some hours). I first assumed it might be related to suspend, however yesterday it also happened without a suspend in between. X.Org X Server 1.18.4 Release Date: 2016-07-19 [ 3671.610] X Protocol Version 11, Revision 0 [ 3671.610] Build Operating System: Linux 4.5.4-1-ARCH x86_64 [ 3671.611] Current Operating System: Linux feder 4.8.8-1-ARCH #1 SMP PREEMPT Tue Nov 15 08:25:24 CET 2016 x86_64 [ 3671.611] Kernel command line: BOOT_IMAGE=/vmlinuz-linux root=UUID=22a059b2-d72f-4d45-8da7-c4cc22b9a620 rw cryptdevice=/dev/nvme0n1p3:root quiet [ 3671.611] Build Date: 19 July 2016 05:54:24PM [10:54] feder:~% pacman -Q | grep ^xorg xorg-appres 1.0.4-1 xorg-bdftopcf 1.0.5-1 xorg-font-util 1.3.1-1 xorg-font-utils 7.6-4 xorg-fonts-alias 1.0.3-1 xorg-fonts-encodings 1.0.4-4 xorg-fonts-misc 1.0.3-4 xorg-luit 1.1.1-2 xorg-mkfontdir 1.0.7-2 xorg-mkfontscale 1.1.2-1 xorg-server 1.18.4-1 xorg-server-common 1.18.4-1 xorg-setxkbmap 1.3.1-1 xorg-xauth 1.0.9-1 xorg-xbacklight 1.2.1-1 xorg-xdpyinfo 1.3.2-1 xorg-xev 1.2.2-1 xorg-xinit 1.3.4-4 xorg-xinput 1.6.2-1 xorg-xkbcomp 1.3.1-1 xorg-xkill 1.0.4-1 xorg-xmodmap 1.0.9-1 xorg-xrandr 1.5.0-1 xorg-xrdb 1.1.0-2 xorg-xset 1.2.3-1 xorg-xsetroot 1.1.1-2 xorg-xwd 1.0.6-1 xorg-xwininfo 1.1.3-1
Created attachment 128038 [details] dmesg
Can you please attach "xrandr --verbose" from after startup and from when the failure occurs?
Created attachment 128047 [details] [review] Loop on EINTR
Created attachment 128048 [details] xrandr-before-still-working
And here is the xrandr output after it doesn't work anymore, though taken from a few minutes ago, before I restarted xorg
Created attachment 128049 [details] xrandr-after-no-backlight
Thanks, that will the (EE) confirm that it should be a failed write causing the backlight to disappear.
Pushed commit bde946054efbc1c7ae1483b84c3b4fa3c2c7e2ec Author: Chris Wilson <chris@chris-wilson.co.uk> Date: Thu Nov 17 19:22:02 2016 +0000 backlight: Protect iface writes against signal interruptions as it should be the right thing to do, regardless of whether it is the root cause here.
Fun fact: since restarting xorg yesterday, I cannot yet reproduce the problem. Neither suspend, nor connecting / disconncting external output seem to reliable cause the problem. Things I have changed since the first report: - upgraded from linux 4.8.8-1 to linux 4.8.8-2 (should not change anything, only enabled / added the randomization flag) - removed /etc/udev/rules.d/90-backlight.rules that I used for modesetting driver+acpibacklight, which contained: SUBSYSTEM=="backlight", ACTION=="add", RUN+="/bin/chgrp video /sys/class/backlight/%k/brightness" SUBSYSTEM=="backlight", ACTION=="add", RUN+="/bin/chmod g+w /sys/class/backlight/%k/brightness" I do not assume that either of both should have interfered with xorg and I am also in the group video, as can be seen below. [17:54] feder:~% id uid=1000(nico) gid=1000(nico) groups=1000(nico),14(uucp),90(network),91(video),92(audio),93(optical),98(power),100(users),150(wireshark),992(docker) However I also remember having some days *with* backlight being present and then vanishing - thus I'll report again, as soon as it vanishes.
I'm presuming it was the interrupted write causing us to disable the backlight...
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