Git Bisect Log:
git bisect start 'drivers/gpu/drm/radeon'
# good: [a0d271cbfed1dd50278c6b06bead3d00ba0a88f9] Linux 3.6
git bisect good a0d271cbfed1dd50278c6b06bead3d00ba0a88f9
# bad: [29594404d7fe73cd80eaa4ee8c43dcc53970c60e] Linux 3.7
git bisect bad 29594404d7fe73cd80eaa4ee8c43dcc53970c60e
# bad: [af026c5bd14cb57b230a63bdee6f73677a06f010] drm/radeon: Fix scratch register 
leak in
IB test.
git bisect bad af026c5bd14cb57b230a63bdee6f73677a06f010
# bad: [9b40e5d8427f12567749978f66e86e5e8fced5ab] drm/radeon: make VM flushs a ring 
operation
git bisect bad 9b40e5d8427f12567749978f66e86e5e8fced5ab
# bad: [86504672f7d79986a8ef618fb120044220e3d1eb] drm/radeon: refactor 
radeon_atif_call
git bisect bad 86504672f7d79986a8ef618fb120044220e3d1eb
# good: [7ff64fcaa7b7ba62d12758e49643f31dd9e90ece] Rename i2f() to int2float(), and 
make it global so one copy can be removed.
git bisect good 7ff64fcaa7b7ba62d12758e49643f31dd9e90ece
# good: [efd4e418f2bb8a8b21f96fd44e775eaf6dd55905] drm/radeon: add a license header 
to radeon_apci.c
git bisect good efd4e418f2bb8a8b21f96fd44e775eaf6dd55905
# good: [910308802c528f8afe864b694d5456fedd0bb18f] drm/radeon: rework legacy 
backlight control
git bisect good 910308802c528f8afe864b694d5456fedd0bb18f

Final output from 'git bisect'
[f3728734ba78310525bf4a361c7787c7c6fa5d40] drm/radeon: add backlight control for 
atom devices (v2)

From 'git visualise':::
[33mcommit f3728734ba78310525bf4a361c7787c7c6fa5d40ESC[m
Author: Alex Deucher <alexander.deucher@amd.com>
Date:   Thu Jul 26 11:32:03 2012 -0400

    drm/radeon: add backlight control for atom devices (v2)

    On systems that use the build in GPU backlight controller,
    we can use atom tables to change the brightness level.

    v2: use firmware flags

    Signed-off-by: Alex Deucher <alexander.deucher@amd.com>