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

Thu Jul 18 08:54:51 CEST 2013

At Thu, 18 Jul 2013 01:00:07 +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.

I don't understand this requirement.  We know that no HDMI/DP is
plugged in.  The problem Paulo has seen is that the power-saving isn't
kicked off just because it's turned off explicitly.  In other words,
this is a system setup issue, after all.

OTOH, if HDMI/DP can be never plugged in, creating a sound device
itself doesn't make sense at all.  If this is the case, we may improve
the audio driver code just to skip the devices with such
configurations. 

> 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.

Yes.  In general, such a force-to-suspend-the-active-stream event
should happen only when the device is really unavailable, but never be
done just for saving power.

Takashi

> 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
> 