[Intel-gfx] drm/i915: Enabling PC8 on Haswell

[Nicolas Kalkhof]

On Thu, Dec 26, 2013 at 02:46:18PM -0800, Paulo Zanoni wrote:
 
> As far as I could check, your PCI ID is 0416, so your machine is not
> ULT. As far as I know, your machine supports only up to PC7 state. I
> may be wrong. Still, I will provide some comments below:

You are right, my machine is not ULT. I suppose PC8 only works on ULT CPUs, correct?

> To get into Pacakge C8 and deeper states you need all screens to be
> disabled. You mentioned X is not running, so what exactly did you do
> to disable all the screens?

Nohting I just logged in from the console with no X running. So all connected screens have to be disabled for the device to reach PC8 state?

> This means: either one or more screens are enabled, or the power well
> is enabled, or both.

Yeah, power well was enabled by mistake. disabled it but no changes.

>> GPU idle: no
> Something is submitting work to the GPU.

No idea what that could be.

> Did you go to the "tunables" tab and switch everything to "good"? All
> devices (not only graphics) need to be properly configured for the
> machine to reach PC8+.

Yeah everything is "good" and still the haswell system is draining 16-18 Watts with no X and no discrete graphics present. That's what puzzels me. Running the exact same Linux/Kernel Configon a Sandy Bridge i7-2620M the power drain is approx 7-8 Watts with power save turned for all tunables. For Haswell powertop shows nice idle states exept the PC states stay at pc2/pc3 and never reach pc7 while Sandy bridge reaches pc7 most of the time.

>> Kernel is 3.13-rc4 from ~danvet/drm-intel/drm-intel-nightly
>> Params are: i915.i915_enable_rc6=1 pcie_aspm=force i915.i915_disable_power_well=0 i915.enable_pc8=1 "acpi_osi=!Windows 2012" acpi_backlight=legacy

> Why are you using all these options for i915? We recommend to stick to
> the defaults since they are the best bug-free setup.

Well, the pcie_aspm=force switch reduces power drain approx 4-5 Watts and the other acpi options need to be there for the keyboard/backlight  to word. I've already removed the i915 params without effect. 


Thanks and Regards
Nic