[RFC] drm dynamic power off support

[Dave Airlie]

On Mon, Sep 10, 2012 at 2:31 PM, Dave Airlie <airlied at gmail.com> wrote:
> For optimus and powerxpress setups where we can explicitly power off
> the GPU I'd like to do this under control of the driver. Now that I've
> added X server support for secondary GPUs, it makes sense to start
> powering them down more often if we can.
>
> I've tested this code on two laptops, one intel/nouveau one intel/radeon
> It works, powertop says I use 5-6W less power.
>
> Caveats:
> There is a race at X server start with platform probing code, if
> the secondary device is off, we the wrong PCI info for it, I've
> got a patch that works around this I'll send to the xorg-devel.
>
> Audio seems to get screwed at least on one machine, we power up
> and the alsa callbacks into snd_hda_intel get called but it can't
> find the hw properly, need to investigate a bit further.
>
> Dave.
>
Hi Takashi,

just wondering how well setup alsa would be for the dGPU powering
up/down a lot more often,
  139.529103] nouveau  [     DRM][0000:01:00.0] resuming display...
[  139.833960] ALSA sound/pci/hda/hda_intel.c:2533 Enabling
0000:01:00.1 via VGA-switcheroo
[  139.844789] snd_hda_intel 0000:01:00.1: Refused to change power
state, currently in D3
[  139.915760] snd_hda_intel 0000:01:00.1: Refused to change power
state, currently in D3
[  140.917437] ALSA sound/pci/hda/hda_intel.c:813 spurious response
0x0:0x3, last cmd=0x301f0500
[  140.917449] ALSA sound/pci/hda/hda_intel.c:813 spurious response
0x0:0x3, last cmd=0x301f0500
[  140.917455] ALSA sound/pci/hda/hda_intel.c:813 spurious response
0x0:0x3, last cmd=0x301f0500
[  140.917460] ALSA sound/pci/hda/hda_intel.c:813 spurious response
0x0:0x3, last cmd=0x301f0500
[  140.917465] ALSA sound/pci/hda/hda_intel.c:813 spurious response
0x0:0x3, last cmd=0x301f0500

is just some of the things I see, if I turn off before snd_hda_intel,
things go badly wrong when
I do power up the dGPU, if I delay the power off until audio is
loaded, I start to see wierd things when pulseaudio starts when the
dGPU is off.

Dave.