Message-ID: <5b55f75f2fc8a783bf2fdaeac80fd5954e16a2c8.camel@mediatek.com>
Date: Tue, 29 Oct 2024 03:04:55 +0000
From: Trevor Wu (吳文良) <Trevor.Wu@...iatek.com>
To: "fshao@...omium.org" <fshao@...omium.org>, AngeloGioacchino Del Regno
	<angelogioacchino.delregno@...labora.com>, "krzk@...nel.org"
	<krzk@...nel.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-sound@...r.kernel.org" <linux-sound@...r.kernel.org>,
	"broonie@...nel.org" <broonie@...nel.org>, "conor+dt@...nel.org"
	<conor+dt@...nel.org>, "robh@...nel.org" <robh@...nel.org>,
	"lgirdwood@...il.com" <lgirdwood@...il.com>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "matthias.bgg@...il.com"
	<matthias.bgg@...il.com>, "krzk+dt@...nel.org" <krzk+dt@...nel.org>
Subject: Re: [PATCH 1/4] ASoC: dt-bindings: mediatek,mt8188-mt6359: Add adsp
 and dai-link properties

On Mon, 2024-10-28 at 15:25 +0100, AngeloGioacchino Del Regno wrote:
> External email : Please do not click links or open attachments until
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> 
> 
> Il 28/10/24 12:10, Fei Shao ha scritto:
> > On Mon, Oct 28, 2024 at 4:54 AM Krzysztof Kozlowski <
> > krzk@...nel.org> wrote:
> > > 
> > > On Fri, Oct 25, 2024 at 06:44:41PM +0800, Fei Shao wrote:
> > > > Add "mediatek,adsp" property for the ADSP handle if ADSP is
> > > > enabled on
> > > > the platform.
> > > 
> > > We see this from the diff.
> > > 
> > > > Add "mediatek,dai-link" property for the required DAI links to
> > > > configure
> > > > sound card.
> > > 
> > > We see this from the diff.
> > > 
> > > > 
> > > > Both properties are commonly used in the MediaTek sound card
> > > > driver.
> > > 
> > > If they are used, why suddenly they are needed? What changed?
> > 
> > Nothing has changed. These should have been added altogether when
> > the
> > binding was first introduced. This patch is to fill the gaps and
> > fix
> > dtbs_check warnings, like I mentioned in the cover letter.
> > I can add a line in the commit message saying it's to fix the
> > warning
> > in addition to the cover letter, if that's preferred.
> > 
> > > 
> > > > 
> > > > Signed-off-by: Fei Shao <fshao@...omium.org>
> > > > ---
> > > > 
> > > >   .../bindings/sound/mediatek,mt8188-mt6359.yaml         | 10
> > > > ++++++++++
> > > >   1 file changed, 10 insertions(+)
> > > > 
> > > > diff --git
> > > > a/Documentation/devicetree/bindings/sound/mediatek,mt8188-
> > > > mt6359.yaml
> > > > b/Documentation/devicetree/bindings/sound/mediatek,mt8188-
> > > > mt6359.yaml
> > > > index f94ad0715e32..701cedfa38d2 100644
> > > > --- a/Documentation/devicetree/bindings/sound/mediatek,mt8188-
> > > > mt6359.yaml
> > > > +++ b/Documentation/devicetree/bindings/sound/mediatek,mt8188-
> > > > mt6359.yaml
> > > > @@ -29,6 +29,16 @@ properties:
> > > >       $ref: /schemas/types.yaml#/definitions/phandle
> > > >       description: The phandle of MT8188 ASoC platform.
> > > > 
> > > > +  mediatek,adsp:
> > > > +    $ref: /schemas/types.yaml#/definitions/phandle
> > > > +    description: The phandle of MT8188 ADSP platform.
> > > 
> > > And what is the difference between ASoC and ADSP platforms? What
> > > are
> > > they used for?
> > 
> > I'm not a MediaTek or audio folks, and I'm afraid that I'm not the
> > best person to explain the details accurately in front of experts
> > on
> > the list... I know it's an audio DSP but that explains nothing.
> > MediaTek didn't provide a meaningful explanation in the tree or
> > commits, and I want to avoid adding additional but likely
> > misleading
> > descriptions from someone who doesn't have enough knowledge,
> > potentially causing even more confusing situations in the future.
> > Plus, the same changes were accepted as-is in the past, so I
> > assumed
> > they might be self-explanatory to people who are familiar with the
> > matter.
> > 
> 
> The Audio DSP is a Tensilica HiFi-5 DSP, and it's a block that is -
> hardware
> speaking - separated from the rest of the Audio interfaces of the
> SoC.
> 
> The whole sound subsystem can work either with or without the DSP, in
> the sense
> that the DSP itself can remain unpowered and completely unconfigured
> if its
> functionality is not desired - hence, this is a board specific
> configuration:
> if the board wants to use the DSP, we use the DSP - otherwise, we
> just don't.
> 
> Regarding the two "platforms", in short:
> "mediatek,platform" -> Audio Front End (AFE)
> "mediatek,adsp" -> Audio DSP
> 
> Now, you can either link the AFE DAIs to the I2S
> 
> As for "mediatek,platform" - that's used to link the Analog Front End
> (AFE) as
> the DAI Link platform (so the path is direct to/from DL/UL DAIs to
> AFE) or the
> ADSP one as the DAI Link platform (so that the path is to/from DL/UL
> DAIs to
> DSP to AFE), but that - of course - still requires an AFE, otherwise
> you cannot
> get the audio out of the speakers or in from the mic anyway.
> 
> > > 
> > > > +
> > > > +  mediatek,dai-link:
> > > > +    $ref: /schemas/types.yaml#/definitions/string-array
> > > > +    description:
> > > > +      A list of the desired dai-links in the sound card. Each
> > > > entry is a
> > > > +      name defined in the machine driver.
> > > 
> > > The list is provided below. I don't understand why do you need
> > > it. Your
> > > msg is pretty useless - you describe what you do, instead of why.
> > 
> > I think this is used to explicitly list the intermediate but hidden
> > DAIs, but again, there's not much info about them unless MediaTek
> > can
> > explain more details and why they need a vendor property for this.
> > 
> 
> Yes, this is used for exactly that... but I believe that we can
> deprecate this
> now that we have support for the "standard" `audio-routing` property
> and for the
> DAI Link nodes (examples that you can find in current device trees
> are mm-dai-link,
> hs-playback-dai-link, or any other subnode of the sound card).
> 
> Specifically, those subnodes *do* require a "link-name" property,
> which *does*
> effectively contain the same DAI Link names as the ones that are
> inside of the
> "mediatek,dai-link" property.
> 
> On MT8195, you can find both the subnodes and the mediatek,dai-link -
> yes - but
> that was done to retain compatibility of the device tree with old
> drivers (so,
> an unusual case of new device tree on old kernel).
> 
> Finally, I believe that we can avoid adding that "mediatek,dai-link"
> property
> to the MT8188 binding, and rely on:
>   1. Whatever is provided in struct snd_soc_card for that device; and
>   2. Whatever is provided in device trees as dai link subnodes, which
> would
>      restrict N.1 as that's anyway describing card prelinks.
> 

The "mediatek,dai-link" property is utilized to hide the unused dai-
links in the sound card. By hiding the unused FE links, it can save the
necessary memory and prevent conflicts where both the DSP and AP
control the same AFE Memifs.

This concept was first implemented in mt8195 as Mark aimed to avoid the
need for a separate driver for different system configurations.
With the introduction of DSP (SOF), if certain AFE Memifs are already
in use in the DSP route, they should be excluded from the PCM nodes
created for the AFE platform.

At that time, we did not have a better way to handle these scenarios,
so we made use of a vendor-defined property.

It has been a while since I last kept up with the updates in mt8188, so
I'm uncertain if the current mechanism for sound card description is
sufficient for handling such scenarios. If it is, I agree that we can
deprecate such a vendor property from mt8188.

Thanks,
Trevor


> Cheers,
> Angelo
> 
> > Regards,
> > Fei
> > 
> > > 
> > > Best regards,
> > > Krzysztof
> > > 
> 
> 

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