linux-kernel - Re: omap4-droid4: voice call support was Re: [PATCHv5,5/5] ARM: dts: omap4-droid4: add soundcard

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Date:   Wed, 28 Mar 2018 16:02:19 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.co.uk>
To:     Mark Brown <broonie@...nel.org>
Cc:     Pavel Machek <pavel@....cz>, Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Tony Lindgren <tony@...mide.com>,
        Lee Jones <lee.jones@...aro.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel@...labora.com
Subject: Re: omap4-droid4: voice call support was Re: [PATCHv5,5/5] ARM: dts:
 omap4-droid4: add soundcard

Hi,

On Wed, Mar 28, 2018 at 10:29:10AM +0800, Mark Brown wrote:
> On Wed, Mar 28, 2018 at 12:22:37AM +0200, Sebastian Reichel wrote:
> > On Tue, Mar 27, 2018 at 08:14:41PM +0800, Mark Brown wrote:
> 
> > > No, this is exactly the sort of use case with multiple DAIs that the
> > > graph card is intended to enable over the old simple-card.
> 
> > +----------+         +-------------+
> > | OMAP4    |         | CPCAP       |
> > |          |         |             |
> > | [McBSP2] | <-----> | [HiFi DAI]  |
> > |          |         |             |
> > | [McBSP3] | <--+--> | [Voice DAI] |
> > |          |    |    |             |
> > +----------+    |    +-------------+
> >                 |
> > +----------+    |    +-------------+
> > | MDM6600  |    |    | WL1285      |
> > |          |    |    |             |
> > |    [DAI] | <--+--> | [DAI]       |
> > |          |         |             |
> > +----------+         +-------------+
> 
> > Legend:
> >     OMAP4   = SoC running Linux
> >     CPCAP   = Audio codec
> >     MDM6600 = Baseband
> >     WL1285  = Bluetooth
> 
> > Re-reading the audio-graph-card binding document I still don't see
> > how the network (OMAP.McBSP3, CPCAP.Voice, MDM6600, WL1285) is
> > supposed to look like. It seems to expect point-to-point DAI
> > connections.
> 
> Ugh, a TDM mux?

Yes, at least that's how I understood Motorola's code.

> That's really unusual and not particularly supported yet, you'd
> need to extend the graph card to do it.  It's where things should
> end up for a generic card though.

Motorola's driver provided the following modes:

OMAP4 <-> CPCAP      (voice recording)
MDM6600 <-> CPCAP    (voice call, CPU not involved)
OMAP4 <-> WL1285     (bluetooth HFP/HSP)
MDM6600 <-> WL1285   (bluetooth voice call)

In case of the last two variants, the bus clock is provided by
CPCAP, so it needs to be enabled for any audio stream. I suppose
the codec <-> codec as part of TDM is out of scope for the graph
card and we need a Droid 4 specific card driver?

-- Sebastian

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