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

[Shengjiu Wang]

Hi Rob

On Wed, Mar 10, 2021 at 10:49 AM Rob Herring <robh at kernel.org> wrote:
>
> 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.

I will modify the descriptions. but here it is a virtual device.  the
mapping in real h/w is cortex M core, Cortex M core controls the SAI,
DMA interface. What we see from Linux side is a audio service
through rpmsg channel.

>
> > 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 <shengjiu.wang at nxp.com>
> > ---
> >  .../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 <shengjiu.wang at nxp.com>
> > +
> > +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?

When the cortex-M core support audio service, these clock
needed prepared & enabled by ALSA driver.

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

Ok, I will remove this minItems.

>
> > +
> > +  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?

I will remove it. it is not necessary

>
> > +
> > +  fsl,version:
>
> version of what?
>
> This seems odd at best.
>

I will remove it.  it is not necessary

> > +    $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?

The DMA is handled by M core image for sound playback
and capture. we need to allocated buffer in Linux side.
here just make the buffer size to be configurable.
>
> > +
> > +  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?

I will add more description:
0: dummy codec
1: WM8960 codec
2: AK4497 codec

>
> > +
> > +  audio-codec:
> > +    $ref: /schemas/types.yaml#/definitions/phandle
> > +    description: The phandle of the audio codec
>
> The codec is controlled from the Linux side?

yes.

>
> > +
> > +  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?

The rpmsg data is not handled in this "rpmsg_audio" device, it is just to
prepare the resource for rpmsg audio function, the clock, the memory
the power...

The rpmsg data is handled in imx-pcm-rpmsg.c and imx-audio-rpmsg.c
These devices is registered by imx remoteproc driver.


I will update this document in v5

Best regards
Wang Shengjiu