linux-kernel - Re: [PATCH V2 1/2] ASoC: dt-bindings: audio-graph-port: Add dai-tdm-slot-width-map

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Message-ID: <YhgCbKzfPXEVauwW@robh.at.kernel.org>
Date:   Thu, 24 Feb 2022 16:10:52 -0600
From:   Rob Herring <robh@...nel.org>
To:     Richard Fitzgerald <rf@...nsource.cirrus.com>
Cc:     broonie@...nel.org, kuninori.morimoto.gx@...esas.com,
        alsa-devel@...a-project.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, patches@...nsource.cirrus.com
Subject: Re: [PATCH V2 1/2] ASoC: dt-bindings: audio-graph-port: Add
 dai-tdm-slot-width-map

On Thu, Feb 17, 2022 at 01:48:34PM +0000, Richard Fitzgerald wrote:
> Some audio hardware cannot support a fixed slot width or a slot width
> equal to the sample width in all cases. This is usually due either to
> limitations of the audio serial port or system clocking restrictions.
> 
> This property allows setting a mapping of sample widths and the
> corresponding tdm slot widths.
> 
> Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
> ---
>  .../devicetree/bindings/sound/audio-graph-port.yaml        | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/sound/audio-graph-port.yaml b/Documentation/devicetree/bindings/sound/audio-graph-port.yaml
> index 476dcb49ece6..420adad49382 100644
> --- a/Documentation/devicetree/bindings/sound/audio-graph-port.yaml
> +++ b/Documentation/devicetree/bindings/sound/audio-graph-port.yaml
> @@ -71,4 +71,11 @@ patternProperties:
>          description: CPU to Codec rate channels.
>          $ref: /schemas/types.yaml#/definitions/uint32
>  
> +      dai-tdm-slot-width-map:
> +        description: Mapping of sample widths to slot widths. For hardware that
> +          cannot support a fixed slot width or a slot width equal to sample

A variable slot width sounds like a feature, not a limitation.

> +          width. An array containing one or more pairs of values. Each pair
> +          of values is a sample_width and the corresponding slot_width.

That sounds like a matrix, not an array. N entries of 2 cells each. 

> +        $ref: /schemas/types.yaml#/definitions/uint32-array
> +

I'd think there are some constraints on the values? Slots should be at 
least 8 bits, right? A max of 2x32 bits or is there more 
than stereo within a slot? In any case, it's for sure no where near 2^32 
max.

Is there a need for specifying where in the slot the data is?

Rob