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[Seth Forshee <seth.forshee+lp@xxxxxxxxxxxxx>]

One more thing. Can you supply the output of running "cat
/sys/class/backlight/acpi_video0/device/firmware_node/path" for both
kernels?

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https://bugs.launchpad.net/bugs/1243267

Title:
  Backlight brightness control doesn't work

Status in “linux” package in Ubuntu:
  Confirmed

Bug description:
  Hello, during a kernel update from 3.11.0-4 up to 3.11.0-9 i've found out that my brightness controll of my Notebook (Lenovo Thinkpad T430-D17 (nvidia-graphic card, optimus disabled, driver version: 325.15) does not work). Therefore, i have tried several kernel from kernel.org where all Kernel provides the backlight control. To get comparable values, i have tried the kernel version 
  ubuntu-kernel: Ubuntu 3.12.0-0.2-generic and 3.12.0-rc6
  By using the the ubuntu kernel, i wasn't able to control the backlight brightness but by using the kernel profided by kernel.org works. Therefore, i began to search the patch lists of ubuntu and find this patch: http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-trusty.git;a=blobdiff;f=drivers/acpi/blacklist.c;h=f49ffaedaefdaa28d533d339a3f5cda073687ed7;hp=9515f18898b2b578053c58309185daa7934cfdda;hb=02cb06962306d96f59bc97ec8289c14b73bafb4e;hpb=2eb9acd1a1deb3f4d6428d022fc43541c9e70069.
  I have reverted this patch and the brightness control of my notebook works fine. 

  If anybody wants to execute the ubuntu-bug program, you should note,
  that i'm not using ubuntu, i'm only using the ubuntu kernel and the
  ubuntu-bug program is not in my repositories. Therefore, i supply the
  lspci-vnvn report. If any other logs or reports are missing please
  feel free to ask me.

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