[PATCH 0/8] arm64: dts: renesas: Simple-Card / Audio-Graph-Card/Card2 dts for ULCB/KF

[Geert Uytterhoeven]

Hi Morimoto-san,

On Thu, Jan 12, 2023 at 1:17 AM Kuninori Morimoto
<kuninori.morimoto.gx at renesas.com> wrote:
> > What is the difference between "Simple Audio Card", "Audio Graph Card",
> > and "Audio Graph Card2"?  Why do we need to support all three of them?
>
> The answer is because of "history" and "compatibility".
>
> "Simple Audio Card" was created before DT support, now it is supporting DT too.
> But it is for very simple sound connection. It is using own DT style.
>
> "Audio Graph Card" is almost same as "Simple Audio Card", but it is
> using "Of Graph" style. It is needed for HDMI support (= Sound with Video).
> "Audio Graph Card" was created because it is difficult to keep compatibility
> for both "Of Graph style" and "own style" on "Simple Audio Card".
>
> "Audio Graph Card2" is expand version of "Audio Graph Card",
> but it is supporting more complex connections.
> Because of this complex connection, it is difficult to keep compatibility
> with "Audio Graph Card".

So they are different ways (generations) of representing the audio
topology on the board? Like "operating-points" and "operating-points-v2"
for cpufreq?

Hence these are orthogonal to (and independent of) the underlying audio
hardware in the SoC?

> For normal user case, selecting one of them is very enough.
> But for me, I need to test all of them, thus I want to switch these easily.
> And ULCB is good board for testing.
>
> Basically, people don't need to care about this patch-set.
> It separates DT file, but nothing change.
> It is just easy for testing.

OK. And I guess you intend to use them as examples to point people
to, too?

> > How come we can have no #sound-dai-cells, #sound-dai-cells = <0>,
> > and #sound-dai-cells = <1>, for the same hardware?
> > What is the real difference between Single DAI and Multi DAI?
> > Why do we need to support both?
>
> It is used on "Simple Audio Card".
> We  need <0> if the board is using SSI x 1,
> and need <1> if the board is using SSI x N.
> It is not mandatory if the board is using "Audio Graph Card/Card2".

So #sound-dai-cells should be in the board DTS, and never in the
SoC .dtsi? Hence it should be moved out of
arch/arm/boot/dts/{r8a7740,sh73a0}.dtsi and
arch/arm64/boot/dts/renesas/r9a07g0{43,44,54}.dtsi?

> > > Kuninori Morimoto (8):
> > >   ARM: dts: renesas: #sound-dai-cells is used when simple-card
> > >   arm64: dts: renesas: #sound-dai-cells is used when simple-card
> > >   arm64: dts: renesas: add ulcb{-kf} Audio Graph Card dtsi
> > >   arm64: dts: renesas: add ulcb{-kf} Audio Graph Card2 dtsi
> > >   arm64: dts: renesas: add ulcb{-kf} Simple Audio Card dtsi
> >
> > The above three all describe the same hardware configuration?
>
> Yes, same hardware, but is using different connection style (= driver).

OK.

> > >   arm64: dts: renesas: add ulcb{-kf} Audio Graph Card2 dtsi MIX + TDM Split dtsi
> > >   arm64: dts: renesas: add ulcb{-kf} Audio Graph Card dtsi MIX + TDM Split dtsi
> > >   arm64: dts: renesas: add ulcb{-kf} Simple Audio Card MIX + TDM Split dtsi
> >
> > Is MIX and TDM Split a different hardware configuration, or software
> > policy?
>
> Same hardware, but different connection (= mixing, split).
>
> Hmm, it is difficult to explain via text...

IC, this is more complicated...

Thanks!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds