[Bug 99126] New: [945GME] wrong scale for backlight with Xfce

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99126

            Bug ID: 99126
           Summary: [945GME] wrong scale for backlight with Xfce
           Product: xorg
           Version: git
          Hardware: x86 (IA32)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/intel
          Assignee: chris at chris-wilson.co.uk
          Reporter: rpnpif at free.fr
        QA Contact: intel-gfx-bugs at lists.freedesktop.org

The scale of change of the intensity of the backlight is wrong.
Changing this is done with the hot keys to increase or decrease.

The minimum get a black screen.
cat /sys/class/backlight/eeepc/brigthness
0
cat /sys/class/backlight/intel_backlight/brigthness
0

1st press on the hot key : get also a black screen.
cat /sys/class/backlight/eeepc/brigthness
1
cat /sys/class/backlight/intel_backlight/brigthness
79787

2nd press : get a medium intensity.
cat /sys/class/backlight/eeepc/brigthness
2
cat /sys/class/backlight/intel_backlight/brigthness
159374

3rd to 12th press get a normal change of the backlight.
To : 796875
But the intensity of the 12th is less than the 11th.

Expected :
The minimum should not light off the screen.
/sys/class/backlight/intel_backlight/brigthness
159374
>From /sys/class/backlight/eeepc/brigthness=1 to 10 or 12, the backlight 
should change linearly without light off.

This buggy behaviour was seen only with Xfce, not with lightdm or the Linux 
console.

Chipset: 945GME
Architecture: X86
Found in version xserver-xorg-video-intel/2:2.99.917+git20161105-1~bpo8+1 from
Debian Jessie-backports.
Works fine with older versions.

Machine:Eeepc 901.
Reproducible : always.

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=846882

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