[Bug 15166] Changing brightness of backlight freezes kernel with radeon kms enabled.

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https://bugzilla.kernel.org/show_bug.cgi?id=15166





--- Comment #48 from Alex Deucher <alexdeucher@gmail.com>  2010-05-05 15:00:30 ---
One of my coworkers who is also experiencing the problem bisected it down to:
f3eee54276dfd1117fd94259f2b4a38388264724:

commit f3eee54276dfd1117fd94259f2b4a38388264724
Author: Yinghai Lu <yinghai@kernel.org>
Date:   Mon Dec 14 11:52:15 2009 +0900

   x86: Gart: fix breakage due to IOMMU initialization cleanup

   This fixes the following breakage of the commit
   75f1cdf1dda92cae037ec848ae63690d91913eac:

   - GART systems that don't AGP with broken BIOS and more than 4GB
     memory are forced to use swiotlb. They can allocate aperture by
     hand and use GART.

   - GART systems without GAP must disable GART on shutdown.

   - swiotlb usage is forced by the boot option,
     gart_iommu_hole_init() is not called, so we disable GART
     early_gart_iommu_check().

   Signed-off-by: Yinghai Lu <yinghai@kernel.org>
   Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
   LKML-Reference:
   <1260759135-6450-3-git-send-email-fujita.tomonori@lab.ntt.co.jp>
   Signed-off-by: Ingo Molnar <mingo@elte.hu>

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