[alsa-devel] [PATCH] ALSA: hda_intel: add AZX_DCAPS_I915_POWERWELL for skl

[Takashi Iwai]

At Mon, 30 Mar 2015 02:47:45 +0000,
Yang, Libin wrote:
> 
> Hi Takashi,
> 
> 
> > -----Original Message-----
> > From: Yang, Libin
> > Sent: Friday, March 27, 2015 4:34 PM
> > To: Takashi Iwai
> > Cc: alsa-devel at alsa-project.org
> > Subject: RE: [alsa-devel] [PATCH] ALSA: hda_intel: add
> > AZX_DCAPS_I915_POWERWELL for skl
> > 
> > Hi Takashi,
> > 
> > 
> > 
> > > -----Original Message-----
> > > From: Takashi Iwai [mailto:tiwai at suse.de]
> > > Sent: Friday, March 27, 2015 4:30 PM
> > > To: Yang, Libin
> > > Cc: alsa-devel at alsa-project.org
> > > Subject: Re: [alsa-devel] [PATCH] ALSA: hda_intel: add
> > > AZX_DCAPS_I915_POWERWELL for skl
> > >
> > > At Fri, 27 Mar 2015 08:25:52 +0000,
> > > Yang, Libin wrote:
> > > >
> > > > Hi Takashi,
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: alsa-devel-bounces at alsa-project.org [mailto:alsa-devel-
> > > > > bounces at alsa-project.org] On Behalf Of Takashi Iwai
> > > > > Sent: Friday, March 27, 2015 4:19 PM
> > > > > To: Yang, Libin
> > > > > Cc: alsa-devel at alsa-project.org
> > > > > Subject: Re: [alsa-devel] [PATCH] ALSA: hda_intel: add
> > > > > AZX_DCAPS_I915_POWERWELL for skl
> > > > >
> > > > > At Fri, 27 Mar 2015 08:02:54 +0000,
> > > > > Yang, Libin wrote:
> > > > > >
> > > > > > Hi Takashi,
> > > > > >
> > > > > >
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: Takashi Iwai [mailto:tiwai at suse.de]
> > > > > > > Sent: Friday, March 27, 2015 3:57 PM
> > > > > > > To: Yang, Libin
> > > > > > > Cc: alsa-devel at alsa-project.org
> > > > > > > Subject: Re: [PATCH] ALSA: hda_intel: add
> > > > > > > AZX_DCAPS_I915_POWERWELL for skl
> > > > > > >
> > > > > > > At Fri, 27 Mar 2015 15:10:04 +0800,
> > > > > > > libin.yang at intel.com wrote:
> > > > > > > >
> > > > > > > > From: Libin Yang <libin.yang at intel.com>
> > > > > > > >
> > > > > > > > HDMI/DP codec on SKL is in the power well.
> > > > > > > > The power well must be turned on before probing the
> > > > > > > > HDMI/DP codec.
> > > > > > > >
> > > > > > > > Signed-off-by: Libin Yang <libin.yang at intel.com>
> > > > > > >
> > > > > > > So, was the previous question clarified?
> > > > > >
> > > > > > Yes, I have confirmed with our silicon team.
> > > > > >
> > > > > > >
> > > > > > > This certainly sucks.  It means that the powerwell is on even
> > > you
> > > > > > > don't use the HDMI/DP at all.  If this is intended as a
> > temporarily
> > > > > > > workaround, it should be mentioned so.  Please give more
> > > > > comments
> > > > > > > and
> > > > > > > backgrounds.
> > > > > >
> > > > > > Yes, as this is added in the skl audio controller, even there is no
> > > > > HDMI/DP
> > > > > > codec, we should also add this flag. Otherwise the HDMI/DP
> > > codec
> > > > > > may not be detected correctly.
> > > > >
> > > > > But it's possible to do it only at probing, not permanently.  If so,
> > > > > we'll have another patch in future.
> > > > >
> > > > > Please write more information in the changelog and resubmit.
> > > >
> > > > Do you mean to add more description in the patch comments?
> > >
> > > Yes.  The hardware design is different from HSW/BDW, thus applying
> > > this isn't straightforward but just a workaround.  I don't know
> > > whether you think it's a temporary workaround or a permanent fix.
> > > Such information must be written there, too.
> > 
> > OK. I see. It seems we need more input from our silicon team
> > for this issue.
> 
> >From our silicon team's comment, it seems we need power on
> the powerwell when detecting and probing the HDMI codec.
> 
> For the skl case (HDMI codec is in powerwell, while controller not),
> my thinking is:
> 
> 1. power on the power well
> 2. read STATESTS to determine the codec_mask
> 3. if codec is not present, power off the power well
>     and remove the flag. (seems we need a new flag)
> 4. if codec is present, we will power on the power well
>     when dealing with HDMI codec.
> 
> What do you think?

Yes, it's also similar to my plan.  My plan has a bit more code
changes for adapting to the new structure:

- Move hda_i915.c code into sound/hda to be used for both legacy and
  new drivers

- Add a reference counter to get/put, so that it can be called from
  both controller and codec drivers

- Move the component from struct hda_intel to hdac_bus, but
  dynamically allocating.  The helper code can check it like

	if (bus->audio_component)
		bus->audio_component->ops->get_power(...)

  (Or the NULL check can be in a helper function)

- get_power() is called at probing as is now

- put_power() is called at the end of azx_probe*()

- There will be two DCAPS flags, one indicating for the old chips that
  need get_power() for runtime PM, and one indicating get_power() only
  for probing.

Now an open question is how to make codec driver to call get_power /
put_power.  To be more clear, currently there is no solid way to allow
the codec driver doing something special before / after
hda_set_power_state().  One may implement a tricky set_power_state()
ops in the codec driver.  Or, we may reimplement pre_resume and
post_suspend patch_ops again.


Takashi