[Bug 83460] New: [radeon regression] Backlight turned off since kernel upgrade

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=83460

          Priority: medium
            Bug ID: 83460
          Assignee: dri-devel at lists.freedesktop.org
           Summary: [radeon regression] Backlight turned off since kernel
                    upgrade
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: spmf2004-freedesktop at yahoo.fr
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: XOrg CVS
         Component: DRM/Radeon
           Product: DRI

Since the upgrade to Ubuntu kernel 3.13.0-35 (from 3.13.0-34), the screen is
very dark to the point it's unusable.
Backlight seems completely turned off. Using the brightness keys doesn't help.
It was working fine with 3.13.0-34.
I found that the offending patch is "drm/radeon: set default bl level to
something reasonable".
I reverted this patch and recompiled 3.13.0-35, and it solved the problem.
I also checked that this problem also affects mainline kernel 3.17rc3.
More technical details can be found on Ubuntu's bugtracker :
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1364148

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