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

[Shengjiu Wang <shengjiu.wang@gmail.com>]

Hi Rob

On Thu, Mar 11, 2021 at 5:12 AM Rob Herring <robh@kernel.org> wrote:
>
> On Wed, Mar 10, 2021 at 6:33 AM Shengjiu Wang <shengjiu.wang@gmail.com> wrote:
> >
> > Hi Rob
> >
> > On Wed, Mar 10, 2021 at 10:49 AM Rob Herring <robh@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.
>
> It's describing the h/w from the view of the OS. It's not important
> that it's a Cortex-M, but how you interface to it whether that's
> shared registers, mailbox, etc. And it's what resources the block uses
> that the OS controls.

ok.

>
> > > > 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@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@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.
>
> Do we set audio buffer sizes for other audio devices in DT? If not,
> why is this special? If so, why is it not common.

No. I will move it to driver.

>
> > > > +  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
>
> I assume the last 2 cases have nodes in DT (pointed to by
> 'audio-codec'), so this is redundant.

Ok, will remove it.

>
> > > > +
> > > > +  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.
>
> Then what is 'memory-region' for? You need that, a mailbox, or ???
> somewhere in DT.
>
The M core can't access all the DDR memory space on some platform,
so use 'memory-region' reserve a specific memory for dma buffer
which M core can access.

best regards
wang shengjiu