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Date:   Wed, 29 Apr 2020 13:55:32 +0200
From:   Maxime Ripard <maxime@cerno.tech>
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     Chen-Yu Tsai <wens@csie.org>,
        =?utf-8?B?Q2zDqW1lbnQgUMOpcm9u?= <peron.clem@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        devicetree <devicetree@vger.kernel.org>,
        Linux-ALSA <alsa-devel@alsa-project.org>,
        Liam Girdwood <lgirdwood@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-sunxi <linux-sunxi@googlegroups.com>,
        Jernej Skrabec <jernej.skrabec@siol.net>,
        Takashi Iwai <tiwai@suse.com>,
        Jaroslav Kysela <perex@perex.cz>,
        Marcus Cooper <codekipper@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [linux-sunxi] Re: Audio sound card name [was [PATCH 4/7] arm64:
 dts: allwinner: a64: Add HDMI audio]
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Hi

(Sorry for ignoring a couple of mails from you, for some reason your mails
didn't end up in my Inbox)

On Wed, Apr 29, 2020 at 11:43:06AM +0100, Robin Murphy wrote:
> On 2020-04-29 9:17 am, Maxime Ripard wrote:
> > On Wed, Apr 29, 2020 at 02:24:00PM +0800, Chen-Yu Tsai wrote:
> > > On Wed, Apr 29, 2020 at 1:11 AM Robin Murphy <robin.murphy@arm.com> w=
rote:
> > > >=20
> > > > On 2020-04-28 5:49 pm, Cl=E9ment P=E9ron wrote:
> > > > > Hi Mark, Rob,
> > > > >=20
> > > > > On Tue, 28 Apr 2020 at 18:04, Maxime Ripard <maxime@cerno.tech> w=
rote:
> > > > > >=20
> > > > > > On Tue, Apr 28, 2020 at 10:54:00AM +0200, Cl=E9ment P=E9ron wro=
te:
> > > > > > > Hi Maxime,
> > > > > > >=20
> > > > > > > On Tue, 28 Apr 2020 at 10:00, Maxime Ripard <maxime@cerno.tec=
h> wrote:
> > > > > > > >=20
> > > > > > > > On Sun, Apr 26, 2020 at 02:04:39PM +0200, Cl=E9ment P=E9ron=
 wrote:
> > > > > > > > > From: Marcus Cooper <codekipper@gmail.com>
> > > > > > > > >=20
> > > > > > > > > Add a simple-soundcard to link audio between HDMI and I2S.
> > > > > > > > >=20
> > > > > > > > > Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
> > > > > > > > > Signed-off-by: Marcus Cooper <codekipper@gmail.com>
> > > > > > > > > Signed-off-by: Cl=E9ment P=E9ron <peron.clem@gmail.com>
> > > > > > > > > ---
> > > > > > > > >    arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi | 21 +++=
++++++++++++++++
> > > > > > > > >    1 file changed, 21 insertions(+)
> > > > > > > > >=20
> > > > > > > > > diff --git a/arch/arm64/boot/dts/allwinner/sun50i-a64.dts=
i b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> > > > > > > > > index e56e1e3d4b73..08ab6b5e72a5 100644
> > > > > > > > > --- a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> > > > > > > > > +++ b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> > > > > > > > > @@ -102,6 +102,25 @@
> > > > > > > > >                 status =3D "disabled";
> > > > > > > > >         };
> > > > > > > > >=20
> > > > > > > > > +     hdmi_sound: hdmi-sound {
> > > > > > > > > +             compatible =3D "simple-audio-card";
> > > > > > > > > +             simple-audio-card,format =3D "i2s";
> > > > > > > > > +             simple-audio-card,name =3D "allwinner,hdmi";
> > > > > > > >=20
> > > > > > > > I'm not sure what the usual card name should be like though=
=2E I would assume that
> > > > > > > > this should be something specific enough so that you're abl=
e to differentiate
> > > > > > > > between boards / SoC so that the userspace can choose a dif=
ferent configuration
> > > > > > > > based on it?
> > > > > > >=20
> > > > > > > I really don't know what we should use here,
> > > > > > > I just have a look at other SoC:
> > > > > > > rk3328: "HDMI"
> > > > > > > rk3399: "hdmi-sound"
> > > > > > > r8a774c0-cat874: "CAT874 HDMI sound"
> > > > > > >=20
> > > > > > > But maybe it's time to introduce proper name:
> > > > > > > What about :
> > > > > > > pat
> > > > > > > sun50i-h6-hdmi
> > > > > >=20
> > > > > > It's pretty much what we've been using for the other sound card=
s we have, so it
> > > > > > makes sense to me.
> > > > >=20
> > > > > I have a question regarding the simple-audio-card,name.
> > > > > In this patch, I would like to introduce a simple-audio-card for =
the
> > > > > Allwinner A64 HDMI.
> > > > >=20
> > > > > What should be the preferred name for this sound card?
> > > > > "sun50i-a64-hdmi" ? "allwinner, sun50i-a64-hdmi" ?
> > > >=20
> > > > I can at least speak for RK3328, and the reasoning there was that a=
s the
> > > > user looking at what `aplay -l` says, I don't give a hoot about wha=
t the
> > > > SoC may be called, I see two cards and I want to know, with the lea=
st
> > > > amount of uncertainty, which one will make the sound come out of the
> > > > port that's labelled "HDMI" on the box ;)
> > >=20
> > > I agree. The user really doesn't care what SoC the system uses. The o=
nly
> > > real requirement is to be able to tell which output the card is relat=
ed
> > > to, i.e. is it onboard or an external DAC, is it analog or HDMI, etc..
> >=20
> > Yeah, but it's exactly the point.
> >=20
> > If we also end up with "HDMI" as our card name, then the userspace has =
no way to
> > tell anymore if it's running from an rk3328 or an allwinner SoC, or som=
ething
> > else entirely. And therefore it cannot really configure anything to wor=
k out of
> > the box anymore.
>=20
> OK, you're a userspace audio application - enlighten me as to what exact
> chip you're running on here, and why you need to know:
>=20
> card 0: HDMI [HDA ATI HDMI]
>=20
> or how about here?
>=20
> card 0: Intel [HDA Intel]
>=20
>=20
> Furthermore, your argument works both ways - if the equivalent (or in com=
mon
> cases like DesignWare IP blocks, exact same) thing across 3 different SoCs
> has 3 different names, then it's that much harder for userspace that wants
> to present a consistent behaviour. I don't know exactly why LibreELEC have
> downstream patches that standardise all the Rockchip ones to "HDMI", but I
> can't help noting that they do.
>=20
> With simple-audio-card we're talking about trivial interfaces that often
> don't expose any controls at all, so there's unlikely to be much
> 'configuration' for userspace to do beyond choosing which card to output =
to.

That's not really true though. simple-audio-card is used when the connection
between the DAIs is simple. It doesn't mean that the configuration of the C=
PU
DAI (i2s controller in that case) or the configuration of the codec are sim=
ple,
and with pretty featureful codecs, between the various muxes and amps, it c=
an
actually be quite difficult to get the combination of controls you need to
change to output something on the output you expected.

Maxime

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