i915 intel_powerclamp consuming 50% cpu kidle_inject

At least since upgrading to Yakkey, my MacBookPro12,1 (13", 2015) seems to respond to increased system heat using only kidle_inject, and not the built-in fan. kidle_inject with kick in rather quickly, especially with the Australian summer starting to be felt, and will render the system near useless.

Doing some investigation, it appears that no fan is registered as a cooling device:

> mjg@payens:~$ grep . /sys/class/thermal/cooling_device*/type
> /sys/class/thermal/cooling_device0/type:Processor
> /sys/class/thermal/cooling_device1/type:Processor
> /sys/class/thermal/cooling_device2/type:Processor
> /sys/class/thermal/cooling_device3/type:Processor
> /sys/class/thermal/cooling_device4/type:intel_powerclamp

Even though one is picked up by applesmc:

> Nov 08 10:08:56 payens kernel: applesmc: key=670 fan=1 temp=35 index=34 acc=0 lux=2 kbd=1

The fan seems to be physically in good condition, I tested it out using the following:

> root@payens:~# echo 6000 > /sys/devices/platform/applesmc.768/fan1_min

Which started it blowing a lot of warm air out.

ProblemType: Bug
DistroRelease: Ubuntu 16.10
Package: linux-image-generic 4.8.0.26.35
ProcVersionSignature: Ubuntu 4.8.0-26.28-generic 4.8.0
Uname: Linux 4.8.0-26-generic x86_64
ApportVersion: 2.20.3-0ubuntu8
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: mjg 3076 F.... pulseaudio
 /dev/snd/controlC0: mjg 3076 F.... pulseaudio
CurrentDesktop: GNOME
Date: Tue Nov 8 13:36:01 2016
HibernationDevice: RESUME=UUID=bc879a1f-ac27-48ae-82dd-3c81b7307dd0
InstallationDate: Installed on 2015-07-22 (475 days ago)
InstallationMedia: Ubuntu-GNOME 15.04 "Vivid Vervet" - Release amd64 (20150422)
Lsusb:
 Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
 Bus 001 Device 003: ID 05ac:0273 Apple, Inc.
 Bus 001 Device 002: ID 05ac:8290 Apple, Inc.
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
MachineType: Apple Inc. MacBookPro12,1
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.8.0-26-generic root=/dev/mapper/ubuntu--gnome--vg-root ro quiet splash acpi_backlight=vendor i915.fastboot=1
RelatedPackageVersions:
 linux-restricted-modules-4.8.0-26-generic N/A
 linux-backports-modules-4.8.0-26-generic N/A
 linux-firmware 1.161
SourcePackage: linux
UpgradeStatus: Upgraded to yakkety on 2016-10-05 (33 days ago)
dmi.bios.date: 09/28/2015
dmi.bios.vendor: Apple Inc.
dmi.bios.version: MBP121.88Z.0167.B14.1509281135
dmi.board.name: Mac-E43C1C25D4880AD6
dmi.board.vendor: Apple Inc.
dmi.board.version: MacBookPro12,1
dmi.chassis.type: 9
dmi.chassis.vendor: Apple Inc.
dmi.chassis.version: Mac-E43C1C25D4880AD6
dmi.modalias: dmi:bvnAppleInc.:bvrMBP121.88Z.0167.B14.1509281135:bd09/28/2015:svnAppleInc.:pnMacBookPro12,1:pvr1.0:rvnAppleInc.:rnMac-E43C1C25D4880AD6:rvrMacBookPro12,1:cvnAppleInc.:ct9:cvrMac-E43C1C25D4880AD6:
dmi.product.name: MacBookPro12,1
dmi.product.version: 1.0
dmi.sys.vendor: Apple Inc.