Comment 15 for bug 555709

Hi everyone,

I discovered a work-around that actually seems to work. It definitely keeps display at proper brightness when I log in. It was posted by 'Kubicle' on kubuntuforums.net.

I have an even more recent version of the kernel than this (-34), and this still fixes it.

What you do is create the file containing the script listed in step 1. ** One thing I will add is to MAKE SURE the file name is '10-thinkpad-backlight.fdi'. He did not have the .fdi on it.

Seems like a good work-around until the kernel really gets fixed.

It works on my T42, Kubuntu 10.04, KDE 4.5 (which, like KDE 4.4.x, still had this display problem until I added this patch).

-Chris Murphy

* * * * * * * * * * * *

kubicle
Kubuntu Veteran

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Posts: 2876

Thinking Inside the Box

Thinkpad backlight brightness bug in recent kernels [INCLUDES WORKAROUND]
« on: April 13, 2010, 01:45:45 am »
Bug Affects:
Thinkpad T41 (and possibly other models)

Kernels:
2.6.32-18 (Not bugged)
2.6.32-19 (Bugged)
2.6.32-20 (Bugged)

Symptoms:
- Display backlight brightness changes to the lowest value once kde starts to load after logging in from kdm (once hal starts)
- Same happens when switching to X session from tty
- Cannot change display brightness with Powerdevil (kde's power manager), any change dims display
- thinkpad extra buttons for changing backlight brightness (Fn+Home, Fn+End) work normally.

Cause:
Difference in lshal output with nonbugged *-18 and bugged *-20 kernels
Quote
165c149
< laptop_panel.num_levels = 8 (0x8) (int)
---
> laptop_panel.num_levels = 1 (0x1) (int)

Workaround:
1. Create a custom hal policy file for forcing laptop_panel.num_levels value to 8:
file '/etc/hal/fdi/policy/10-thinkpad-backlight' contents:
Quote
<?xml version="1.0" encoding="ISO-8859-1"?> <!-- -*- SGML -*- -->
<deviceinfo version="0.2">
  <device>
    <match key="info.category" string="laptop_panel">
      <match key="linux.sysfs_path" suffix="/backlight/thinkpad_screen">
         <merge key="laptop_panel.num_levels" type="int">8</merge>
      </match>
    </match>
  </device>
</deviceinfo>
2. Relog to restart hal

Remaining Issues:
Powerdevil display brightness slider still doesn't work as expected, but other issues should be fixed.
This is just a workaround and not a definite fix (seems something was changed between *-18 and *-19 kernel, and everything hasn't catched up with the change yet)