Bug 81991

Summary: openSuSE kernel-desktop-3.15.8-2.1.g258e3b0.x86_64 causes horrible backlight flicker - Radeon 1250
Product: Drivers Reporter: David C. Rankin (drankinatty)
Component: Video(DRI - non Intel)Assignee: Alex Deucher (alexdeucher)
Status: CLOSED CODE_FIX    
Severity: normal CC: aaron.lu, alan, alexdeucher
Priority: P1    
Hardware: All   
OS: Linux   
Kernel Version: 3.15.8 Subsystem:
Regression: No Bisected commit-id:

Description David C. Rankin 2014-08-08 21:58:29 UTC 
Yesterday, updating openSuSE 13.1 from http://download.opensuse.org/repositories/Kernel:/stable/standard/ , I pulled in the updated kernel:

kernel-desktop-3.15.8-2.1.g258e3b0.x86_64

  This was an update from:
  
kernel-desktop-3.15.6-2.1.gedc5ddf.x86_64

  Every 1-2 seconds the backlight flickers horribly. It makes the laptop unusable. (related to bug report of ACPI backlight keyboard keys not controlling backlight: https://bugzilla.novell.com/show_bug.cgi?id=887629 ?). 

  The flicker starts as soon as the kernel is booted, is present during the splash screen and remain unchanged after the display and window managers load -- so it is kernel/module related and not desktop related... Booting back into kernel-desktop-3.15.6-2.1.gedc5ddf.x86_64 and all is fine. 
  
  This is on a Toshiba p205d [AMD/ATI] RS690M [Radeon Xpress 1200/1250/1270]. I have never seen backlight flicker before on this laptop and dropping back to 3.15.6 all is fine. 

  Discussion with one of the openSuSE kernel maintainers suggested commit be907c8468c9f47882036109ba550cd2748b86a0 (drm/radeon: set default bl level to something reasonable) may be part of the problem.

  Let me know what all additional information you need and I'll be glad to get it for you.
Comment 1 Aaron Lu 2014-08-12 07:48:10 UTC 
If building the kernel is possible - that can be verified by building the first kernel with the said commit as the HEAD and the second kernel with the said commit removed. Something like this:
$ git clone http://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
$ git checkout -b tmp be907c8468c9f47882036109ba550cd2748b86a0
build kernel and test (this is the 1st kernel)
$ git reset --hard HEAD~1
build kernel and test (this is the 2nd kernel)

If that fails, do a git bisect between v3.15.6 and v3.15.8 to find the offending commit.