[RFC] drm dynamic power off support

[Takashi Iwai]

At Mon, 10 Sep 2012 15:04:02 +1000,
Dave Airlie wrote:
> 
> 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

These come from PCI core, and...

> [  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

These are from hda-codec.  The verb 0x301f0500 is GET_POWER_STATE
verb, so it looks like that the hardware doesn't respond to any h/w
state query / change.

> 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.

What does your patch do?  Sorry, I still haven't followed your patch
yet.

The message from PCI core makes me wonder whether the GPU is really
active at that point.  Since it's just a call of
pci_set_power_state(PCI_D0) at the beginning of resume procedure, it's
rather a problem in a deeper level than the audio controller itself.
The following spurious response messages are likely the result of the
controller being still in D3.


thanks,

Takashi