Re: [PATCH v4 09/10] dt-bindings: display: rockchip: dw-dp: Fix sound DAI cells

[Sebastian Reichel <sebastian.reichel@collabora.com>]

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Hi,

On Wed, Jul 22, 2026 at 09:22:03AM +0200, Krzysztof Kozlowski wrote:
> > diff --git a/Documentation/devicetree/bindings/display/rockchip/rockchip,dw-dp.yaml b/Documentation/devicetree/bindings/display/rockchip/rockchip,dw-dp.yaml
> > index 2b0d9e23e943..c4f8959dd65d 100644
> > --- a/Documentation/devicetree/bindings/display/rockchip/rockchip,dw-dp.yaml
> > +++ b/Documentation/devicetree/bindings/display/rockchip/rockchip,dw-dp.yaml
> > @@ -25,7 +25,7 @@ description: |
> >    * Supports up to 8/10 bits per color component
> >    * Supports RBG, YCbCr4:4:4, YCbCr4:2:2, YCbCr4:2:0
> >    * Pixel clock up to 594MHz
> > -  * I2S, SPDIF audio interface
> > +  * I2S, S/PDIF audio interface
> >  
> >  properties:
> >    compatible:
> > @@ -46,7 +46,7 @@ properties:
> >        - description: DisplayPort AUX clock
> >        - description: HDCP clock
> >        - description: I2S interface clock
> > -      - description: SPDIF interfce clock
> > +      - description: S/PDIF interfce clock
> >  
> >    clock-names:
> >      minItems: 3
> > @@ -83,7 +83,8 @@ properties:
> >      maxItems: 1
> >  
> >    "#sound-dai-cells":
> > -    const: 0
> > +    const: 1
> > +    description: 0 for I2S, 1 for S/PDIF
> 
> This is ABI change, which might be backwards compatible or not, but
> commit msg should explain that. I can easily imagine drivers where
> written that way that they will fail with an old DTB.

It sure is an ABI break on paper, but I don't think it makes sense
to have an enum allowing 0 or 1.

mainline kernel:
At the moment mainline RK3576 dtsi does not have any
#sound-dai-cells in its DP node and RK3588 has it set to <0>
(Which will complain after this change. I have a fix for that
updating it to <1>). But the mainline kernel has absolutely no
driver support for audio and doesn't use the property at all.
Not having the cell means the driver would have to assume that
either I2S or S/PDIF is meant implicitly. But that is also not
documented.

vendor kernel:
The only other driver for the DP controller that I am aware of is
from the vendor kernel tree. That does have #sound-dai-cells = 1 on
RK3588 and uses subnodes for RK3576 (and thus no #sound-dai-cells at
all).

Thus I argue this is a theoretical ABI break, which affects nothing.
I will look into adding this info to the commit message after
dropping the other ideas for <2> and the subnodes.

Greetings,

-- Sebastian

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