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

[Takashi Iwai]

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.


Takashi