Comparing two Debian kernels:
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$ uname -rv
3.2.0-4-powerpc64 #1 SMP Debian 3.2.41-2
$ lsmod | grep windfarm
windfarm_cpufreq_clamp 4265 1
windfarm_max6690_sensor 6030 1
windfarm_lm75_sensor 6521 1
windfarm_smu_sensors 7587 1
windfarm_smu_controls 7770 7
windfarm_pm112 14636 0
windfarm_smu_sat 8271 5 windfarm_pm112
windfarm_pid 4095 1 windfarm_pm112
windfarm_core 12117 7 windfarm_smu_sat,windfarm_pm112,windfarm_smu_controls,windfarm_smu_sensors,windfarm_lm75_sensor,windfarm_max6690_sensor,windfarm_cpufreq_clamp
$ dmesg | grep windfarm
[ 5.184978] windfarm: initializing for dual-core desktop G5
[ 10.488713] windfarm: CPUs control loops started.
[ 13.914914] windfarm: Backside control loop started.
[ 13.965432] windfarm: Slots control loop started.
[ 14.070479] windfarm: Drive bay control loop started.
$ ls /sys/devices/platform/windfarm.0/
backside-fan cpufreq-clamp cpu-power-1 cpu-temp-1 driver slots-fan
backside-temp cpu-front-fan-0 cpu-rear-fan-0 cpu-voltage-0 hd-temp slots-power
cpu-current-0 cpu-front-fan-1 cpu-rear-fan-1 cpu-voltage-1 modalias subsystem
cpu-current-1 cpu-power-0 cpu-temp-0 drive-bay-fan power uevent
$ cat /sys/devices/platform/windfarm.0/cpu-front-fan-*
524
524
$ cat /sys/devices/platform/windfarm.0/cpu-rear-fan-*
562
562
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$ uname -rv
3.10-1-powerpc64 #1 SMP Debian 3.10.3-1 (2013-07-27)
$ lsmod | grep windfarm
windfarm_cpufreq_clamp 4001 1
windfarm_max6690_sensor 4843 0
windfarm_lm75_sensor 5305 0
windfarm_smu_sensors 7691 1
windfarm_smu_controls 7954 7
windfarm_pm112 14588 0
windfarm_smu_sat 8348 1 windfarm_pm112
windfarm_pid 3975 1 windfarm_pm112
windfarm_core 12029 7 windfarm_cpufreq_clamp,windfarm_pm112,windfarm_smu_sensors,windfarm_smu_sat,windfarm_lm75_sensor,windfarm_max6690_sensor,windfarm_smu_controls
$ dmesg | grep windfarm
[ 5.130698] windfarm: initializing for dual-core desktop G5
$ ls /sys/devices/platform/windfarm.0/
backside-fan cpu-front-fan-0 cpu-rear-fan-0 drive-bay-fan modalias slots-fan subsystem
cpufreq-clamp cpu-front-fan-1 cpu-rear-fan-1 driver power slots-power uevent
$ cat /sys/devices/platform/windfarm.0/cpu-front-fan-*
0 RPM
0 RPM
$ cat /sys/devices/platform/windfarm.0/cpu-rear-fan-*
0 RPM
0 RPM
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You can help a lot, if you can build and upload kernel packages for vanilla 3.5.x, 3.6.x, 3.7.x, and 3.8.x. That's how we can find a working one ("good") kernel very fast. Then we can bisect kernel git source repo for first "bad" commit.