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

[Wang, Xingchao]

> -----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.

> 
> 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".

Thanks
--xingchao
> 
> 
> Takashi