Subject: Re: [PATCH v4 3/6] ASoC: dt-bindings: fsl_rpmsg: Add binding doc for rpmsg cpu dai driver

From: Rob Herring <[email-masked]>
Date: Tue, 9 Mar 2021 19:48:34 -0700

On Mon, Mar 08, 2021 at 09:22:27PM +0800, Shengjiu Wang wrote:
> fsl_rpmsg cpu dai driver is driver for rpmsg audio, which is mainly used

Bindings describe h/w blocks, not drivers.

> for getting the user's configuration from device tree and configure the
> clocks which is used by Cortex-M core. So in this document define the
> needed property.
> 
> Signed-off-by: Shengjiu Wang <[email-masked]>
> ---
>  .../devicetree/bindings/sound/fsl,rpmsg.yaml  | 118 ++++++++++++++++++
>  1 file changed, 118 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/sound/fsl,rpmsg.yaml
> 
> diff --git a/Documentation/devicetree/bindings/sound/fsl,rpmsg.yaml b/Documentation/devicetree/bindings/sound/fsl,rpmsg.yaml
> new file mode 100644
> index 000000000000..5731c1fbc0a6
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/sound/fsl,rpmsg.yaml
> @@ -0,0 +1,118 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/sound/fsl,rpmsg.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: NXP Audio RPMSG CPU DAI Controller
> +
> +maintainers:
> +  - Shengjiu Wang <[email-masked]>
> +
> +description: |
> +  fsl_rpmsg cpu dai driver is virtual driver for rpmsg audio, which doesn't
> +  touch hardware. It is mainly used for getting the user's configuration
> +  from device tree and configure the clocks which is used by Cortex-M core.
> +  So in this document define the needed property.
> +
> +properties:
> +  compatible:
> +    enum:
> +      - fsl,imx7ulp-rpmsg
> +      - fsl,imx8mn-rpmsg
> +      - fsl,imx8mm-rpmsg
> +      - fsl,imx8mp-rpmsg
> +
> +  model:
> +    $ref: /schemas/types.yaml#/definitions/string
> +    description: User specified audio sound card name
> +
> +  clocks:
> +    items:
> +      - description: Peripheral clock for register access
> +      - description: Master clock
> +      - description: DMA clock for DMA register access
> +      - description: Parent clock for multiple of 8kHz sample rates
> +      - description: Parent clock for multiple of 11kHz sample rates
> +    minItems: 5

If this doesn't touch hardware, what are these clocks for?

You don't need 'minItems' unless it's less than the number of 'items'.

> +
> +  clock-names:
> +    items:
> +      - const: ipg
> +      - const: mclk
> +      - const: dma
> +      - const: pll8k
> +      - const: pll11k
> +    minItems: 5
> +
> +  power-domains:
> +    maxItems: 1
> +
> +  fsl,audioindex:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    enum: [0, 1]
> +    default: 0
> +    description: Instance index for sound card in
> +                 M core side, which share one rpmsg
> +                 channel.

We don't do indexes in DT. What's this numbering tied to?

> +
> +  fsl,version:

version of what?

This seems odd at best.

> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    enum: [1, 2]

You're going to update this with every new firmware version?

> +    default: 2
> +    description: The version of M core image, which is
> +                 to make driver compatible with different image.
> +
> +  fsl,buffer-size:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description: pre allocate dma buffer size

How can you have DMA, this doesn't touch h/w?

> +
> +  fsl,enable-lpa:
> +    $ref: /schemas/types.yaml#/definitions/flag
> +    description: enable low power audio path.
> +
> +  fsl,rpmsg-out:
> +    $ref: /schemas/types.yaml#/definitions/flag
> +    description: |
> +      This is a boolean property. If present, the transmitting function
> +      will be enabled.
> +
> +  fsl,rpmsg-in:
> +    $ref: /schemas/types.yaml#/definitions/flag
> +    description: |
> +      This is a boolean property. If present, the receiving function
> +      will be enabled.
> +
> +  fsl,codec-type:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    enum: [0, 1, 2]
> +    default: 0
> +    description: Sometimes the codec is registered by
> +                 driver not by the device tree, this items
> +                 can be used to distinguish codecs.

How does one decide what value to use?

> +
> +  audio-codec:
> +    $ref: /schemas/types.yaml#/definitions/phandle
> +    description: The phandle of the audio codec

The codec is controlled from the Linux side?

> +
> +  memory-region:
> +    $ref: /schemas/types.yaml#/definitions/phandle
> +    description: phandle to the reserved memory nodes
> +
> +required:
> +  - compatible
> +  - fsl,audioindex
> +  - fsl,version
> +  - fsl,buffer-size
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    rpmsg_audio: rpmsg_audio {
> +        compatible = "fsl,imx8mn-rpmsg";
> +        fsl,audioindex = <0> ;
> +        fsl,version = <2>;
> +        fsl,buffer-size = <0x6000000>;
> +        fsl,enable-lpa;

How does this work? Don't you need somewhere to put the 'rpmsg' data?

> +    };
> -- 
> 2.27.0