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    <head>
      <base href="https://bugs.freedesktop.org/">
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    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - Backlight settings vanish after some time"
   href="https://bugs.freedesktop.org/show_bug.cgi?id=98759">98759</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Backlight settings vanish after some time
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>xorg
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>unspecified
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>Other
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>All
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>medium
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>Driver/intel
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>chris@chris-wilson.co.uk
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>nico-freedesktop.org@schottelius.org
          </td>
        </tr>

        <tr>
          <th>QA Contact</th>
          <td>intel-gfx-bugs@lists.freedesktop.org
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Created <span class=""><a href="attachment.cgi?id=128037" name="attach_128037" title="xorg.0.0log">attachment 128037</a> <a href="attachment.cgi?id=128037&action=edit" title="xorg.0.0log">[details]</a></span>
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</pre>
        </div>
      </p>


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