[Intel-gfx] [alsa-devel] [PATCH 0/4 V7] Power-well API implementation for Haswell

Thu Jul 18 08:44:15 CEST 2013

On Thu, Jul 18, 2013 at 01:00:07AM +0000, Wang, Xingchao wrote:
> Hi Paulo/Daniel,
> 
> Do you agree to export an API in gfx side for eDP case? 
> Basically the api will let audio drver know which pipe in use. i.e. in the eDP only caes, audio driver
> Will know gfx is not using HDMI/DP and would like to let power-well off. 
> As there's the conflict when user expect display audio driver always active but gfx need audio driver off.
> Audio driver could make decision to release power-well if it knows the eDP only case through the API.
> 
> OTOH, I think audio driver could also export an API for gfx side, if gfx driver need audio driver release power-well but it's in usage,
> It will call this API and audio drvier will release power-well accordingly. 
> 
> This change make HDMI/DP hotplug handling complicated in audio driver side, if audio driver release power-well, it would enter suspend mode.
> Meanwhile the user may expect it's in active mode, this may cause some confuse.

Afaik (and I know very little about audio) the audio side already knows
which pipes have audio enabled, since we set the respective bit only when
it's needed. And audio will receive the unsolicited even interrupt (or
whatever it's called) when this happens.

So I think we already have the means (albeit with that quirky hw
interface, but it seems to have been good enough for a long time already)
to do that. Or do I miss something?
-Daniel

> 
> Thanks
> --xingchao
> 
> > -----Original Message-----
> > From: Wang, Xingchao
> > Sent: Thursday, July 18, 2013 7:18 AM
> > To: 'Takashi Iwai'; David Henningsson; Paulo Zanoni
> > Cc: alsa-devel at alsa-project.org; Daniel Vetter; daniel.vetter at ffwll.ch;
> > intel-gfx at lists.freedesktop.org; Wang xingchao; Girdwood, Liam R; Jin, Gordon
> > Subject: RE: [alsa-devel] [Intel-gfx] [PATCH 0/4 V7] Power-well API
> > implementation for Haswell
> > 
> > 
> > 
> > > -----Original Message-----
> > > From: Takashi Iwai [mailto:tiwai at suse.de]
> > > Sent: Wednesday, July 17, 2013 10:22 PM
> > > To: David Henningsson
> > > Cc: Paulo Zanoni; Wang, Xingchao; alsa-devel at alsa-project.org; Daniel
> > > Vetter; daniel.vetter at ffwll.ch; intel-gfx at lists.freedesktop.org; Wang
> > > xingchao; Girdwood, Liam R; Jin, Gordon
> > > Subject: Re: [alsa-devel] [Intel-gfx] [PATCH 0/4 V7] Power-well API
> > > implementation for Haswell
> > >
> > > At Wed, 17 Jul 2013 16:05:43 +0200,
> > > David Henningsson wrote:
> > > >
> > > > On 07/17/2013 04:00 PM, Takashi Iwai wrote:
> > > > > At Wed, 17 Jul 2013 10:31:26 -0300, Paulo Zanoni wrote:
> > > > >>
> > > > >> 2013/7/17 Wang, Xingchao <xingchao.wang at intel.com>:
> > > > >>>
> > > > >>>
> > > > >>>> -----Original Message-----
> > > > >>>> From: Takashi Iwai [mailto:tiwai at suse.de]
> > > > >>>> Sent: Wednesday, July 17, 2013 4:18 PM
> > > > >>>> To: Wang, Xingchao
> > > > >>>> Cc: Paulo Zanoni; alsa-devel at alsa-project.org; Daniel Vetter;
> > > > >>>> daniel.vetter at ffwll.ch; intel-gfx at lists.freedesktop.org; Wang
> > > > >>>> xingchao; Girdwood, Liam R; david.henningsson at canonical.com
> > > > >>>> Subject: Re: [alsa-devel] [Intel-gfx] [PATCH 0/4 V7] Power-well
> > > > >>>> API implementation for Haswell
> > > > >>>>
> > > > >>>> At Wed, 17 Jul 2013 08:03:38 +0000, Wang, Xingchao wrote:
> > > > >>>>>
> > > > >>>>>
> > > > >>>>>
> > > > >>>>>> -----Original Message-----
> > > > >>>>>> From: Takashi Iwai [mailto:tiwai at suse.de]
> > > > >>>>>> Sent: Wednesday, July 17, 2013 3:34 PM
> > > > >>>>>> To: Wang, Xingchao
> > > > >>>>>> Cc: Paulo Zanoni; alsa-devel at alsa-project.org; Daniel Vetter;
> > > > >>>>>> daniel.vetter at ffwll.ch; intel-gfx at lists.freedesktop.org; Wang
> > > > >>>>>> xingchao; Girdwood, Liam R; david.henningsson at canonical.com
> > > > >>>>>> Subject: Re: [alsa-devel] [Intel-gfx] [PATCH 0/4 V7]
> > > > >>>>>> Power-well API implementation for Haswell
> > > > >>>>>>
> > > > >>>>>> At Wed, 17 Jul 2013 02:52:41 +0000, Wang, Xingchao wrote:
> > > > >>>>>>>
> > > > >>>>>>> Hi Takashi/Paulo,
> > > > >>>>>>>
> > > > >>>>>>>>>> would you change it to "auto" and test again.
> > > > >>>>>>>>>> Runtime power save should be enabled with "auto".
> > > > >>>>>>>>>
> > > > >>>>>>>>> Doesn't solve the problem. Should I open a bug report
> > > somewhere?
> > > > >>>>>>>>> Having the power well enabled prevents some power saving
> > > > >>>>>>>>> features from the graphics driver.
> > > > >>>>>>>>
> > > > >>>>>>>> Is the HD-audio power-saving itself working?  You can check
> > > > >>>>>>>> it via watching /sys/class/hwC*/power_{on|off}_acct files.
> > > > >>>>>>>>
> > > > >>>>>>>> power_save option has to be adjusted appropriately.  Note
> > > > >>>>>>>> that many DEs change this value dynamically per AC-cable
> > > > >>>>>>>> plug/unplug depending on the configuration, and often it's
> > > > >>>>>>>> set to 0 (= no power save) when AC-cable is plugged.
> > > > >>>>>>>>
> > > > >>>>>>> [Wang, Xingchao] Paulo used a new Ultrabook board with
> > > > >>>>>>> charger connected,
> > > > >>>>>> and see the default parameter "auto=on".
> > > > >>>>>>> In such scenario, power-well is always occupied by Display
> > > > >>>>>>> audio controller. Moreover, in this board, if no external
> > > > >>>>>>> monitors connected, It's
> > > > >>>>>> using internal eDP and totally no audio support. Power-well
> > > > >>>>>> usage in such case also blocks some eDP features as Paulo told me.
> > > > >>>>>>>
> > > > >>>>>>> So I think it's not a good idea to break the rule of power
> > > > >>>>>>> policy when charger
> > > > >>>>>> connected but it's necessary to add support in this particular case.
> > > > >>>>>>> Takashi, do you think it's acceptable to let Display audio
> > > > >>>>>>> controller/codec
> > > > >>>>>> suspend in such case?
> > > > >>>>>>
> > > > >>>>>> Do you mean the driver enables the powersave forcibly?
> > > > >>>>>
> > > > >>>>> Yes. I mean call pm_runtime_allow() for the power-well HD-A
> > > controller.
> > > > >>>>>
> > > > >>>>>> Then, no, not in general.
> > > > >>>>>>
> > > > >>>>>> If the default parameter of autopm is the problem, this
> > > > >>>>>> should be changed, instead of forcing the policy in the driver.
> > > > >>>>>>
> > > > >>>>>> OTOH, the audio codec's powersave policy is governed by the
> > > > >>>>>> power_save option and it's set up dynamically by the desktop
> > system.
> > > > >>>>>> We shouldn't override it in the driver.
> > > > >>>>>>
> > > > >>>>>> If the power well *must* be off when only an eDP is used (e.g.
> > > > >>>>>> otherwise the hardware doesn't work properly), then it's a
> > > > >>>>>> different story.  Is it the case?   And what exactly would be the
> > > > >>>>>> problem?
> > > > >>>>> In the eDP only case, no audio is needed for the HD-A
> > > > >>>>> controller, so it's
> > > > >>>> wasting power in current design.
> > > > >>>>> I think Paulo or Daniel could explain more details on the impact.
> > > > >>>>
> > > > >>>> Consuming more power is the expected behavior.  What else?
> > > > >>>>
> > > > >>>>
> > > > >>>>>> If it's the case, controlling the power well based on the
> > > > >>>>>> runtime PM is likely a bad design, as it relies on the
> > > > >>>>>> parameter user
> > > sets.
> > > > >>>>>> (And remember that the power-saving of the audio can be
> > > > >>>>>> disabled completely via Kconfig, too.)
> > > > >>>>>  From audio controller's point of view, if it's asked be
> > > > >>>>> active, it needs power
> > > > >>>> and should request power-well from gfx side.
> > > > >>>>> In above case, audio controller should not be active but user
> > > > >>>>> set it be
> > > > >>>> "active".
> > > > >>>>
> > > > >>>> By setting the autopm "on", user expects that no runtime PM
> > happens.
> > > > >>>> In other words, the audio controller must be kept active as
> > > > >>>> long as this parameter is set.  And this is the parameter user
> > > > >>>> controls, and not what the driver forcibly sets.
> > > > >>>
> > > > >>> Okay, become clear now. :)
> > > > >>> So I think the conflict for Paulo becomes, in eDP caes, if audio
> > > > >>> is active
> > > and requested power-well, some eDP feature was under impact?
> > > > >>> Paulo, would you clarify this in more details?
> > > > >>
> > > > >> On our driver we try to disable the power well whenever possible,
> > > > >> as soon as possible. We don't change our behavior based on power
> > > > >> AC or other user-space modifiable behavior (except the
> > > > >> i915.disable_power_well Kernel option). If the power well is not
> > > > >> disabled we can't enable some features, like PSR (panel self
> > > > >> refresh, and eDP feature) or PC8, which is another power-saving
> > > > >> feature. This will also make our QA procedures a lot more complex
> > > > >> since when we want to test specific features (e.g., PSR, PC8)
> > > > >> we'll have to disconnect the AC adapter or run scripts. So the
> > > > >> behavior/predictability of our driver will be based on the Audio
> > > > >> driver
> > > power management policies.
> > > > >
> > > > > So all missing feature are about the power saving?
> > > > >
> > > > >> I am not so experienced with general Linux Power Management code,
> > > > >> so maybe the way the Audio driver is behaving is just the usual
> > > > >> way, but I have to admit I was expecting the audio driver would
> > > > >> only require the power well when it is actually needed, and
> > > > >> release it as soon as possible.
> > > > >
> > > > > It would behave so, if all setups are for power-saving.
> > > > >
> > > > > But, in your case, the runtime PM control attribute shows "on"; it
> > > > > implies that the runtime PM is effectively disabled, thus
> > > > > disabling power well is also impossible (because it would require
> > > > > turning off the audio controller, too).
> > > >
> > > > So, if the machine only has an eDP (which has no audio function in
> > > > itself, right?) and never HDMI, DP output because there are no such
> > > > physical ports, the audio controller has no function.
> > > > Maybe we can, before doing anything else, ask the video driver first
> > > > if this is the case, and if so, never create the sound card at all,
> > > > and just leave things the way the video driver wants?
> > >
> > > Well, doesn't BIOS mark HDMI/DP audio pins as unused?  Then the audio
> > > driver won't create any instances.  Of course, we can optimize such a
> > > case, indeed.
> > 
> > As I know, the eDP only case doesnot mean no HDMI/DP support. User would
> > plug in HDMI/DP monitor at any time.
> > So diable audio controller totoally is not a good idea. :(.
> > Paulo, is that correct for you case?
> > 
> > --xingchao
> > >
> > >
> > > Takashi

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch