linux-kernel - Re: [PATCH v4 06/28] dt-bindings: net: Add support for QMC HDLC

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Date:   Thu, 24 Aug 2023 18:12:40 +0200
From:   Herve Codina <herve.codina@...tlin.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew@...n.ch>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, Lee Jones <lee@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Qiang Zhao <qiang.zhao@....com>, Li Yang <leoyang.li@....com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Shengjiu Wang <shengjiu.wang@...il.com>,
        Xiubo Li <Xiubo.Lee@...il.com>,
        Fabio Estevam <festevam@...il.com>,
        Nicolin Chen <nicoleotsuka@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>, netdev@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, alsa-devel@...a-project.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v4 06/28] dt-bindings: net: Add support for QMC HDLC

On Mon, 21 Aug 2023 15:42:58 -0500
Rob Herring <robh@...nel.org> wrote:

> On Fri, Aug 18, 2023 at 06:39:00PM +0200, Christophe Leroy wrote:
> > From: Herve Codina <herve.codina@...tlin.com>
> > 
> > The QMC (QUICC mutichannel controller) is a controller present in some
> > PowerQUICC SoC such as MPC885.
> > The QMC HDLC uses the QMC controller to transfer HDLC data.
> > 
> > Additionally, a framer can be connected to the QMC HDLC.
> > If present, this framer is the interface between the TDM bus used by the
> > QMC HDLC and the E1/T1 line.
> > The QMC HDLC can use this framer to get information about the E1/T1 line
> > and configure the E1/T1 line.
> > 
> > Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> > Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> > ---
> >  .../devicetree/bindings/net/fsl,qmc-hdlc.yaml | 46 +++++++++++++++++++
> >  1 file changed, 46 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/net/fsl,qmc-hdlc.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/net/fsl,qmc-hdlc.yaml b/Documentation/devicetree/bindings/net/fsl,qmc-hdlc.yaml
> > new file mode 100644
> > index 000000000000..13f3572f0feb
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/net/fsl,qmc-hdlc.yaml
> > @@ -0,0 +1,46 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/net/fsl,qmc-hdlc.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Freescale/NXP QUICC Multichannel Controller (QMC) HDLC
> > +
> > +maintainers:
> > +  - Herve Codina <herve.codina@...tlin.com>
> > +
> > +description: |  
> 
> Don't need '|'

Will be fixed in the next iteration.

> 
> > +  The QMC HDLC uses a QMC (QUICC Multichannel Controller) channel to transfer
> > +  HDLC data.
> > +
> > +properties:
> > +  compatible:
> > +    const: fsl,qmc-hdlc
> > +
> > +  fsl,qmc-chan:
> > +    $ref: /schemas/types.yaml#/definitions/phandle-array
> > +    items:
> > +      - items:
> > +          - description: phandle to QMC node
> > +          - description: Channel number
> > +    description:
> > +      Should be a phandle/number pair. The phandle to QMC node and the QMC
> > +      channel to use.
> > +
> > +  framer:
> > +    $ref: /schemas/types.yaml#/definitions/phandle
> > +    description:
> > +      phandle to the framer node  
> 
> What's the framer? 

A framer is a component in charge of an E1/T1 line interface.
Is is connected to the TDM bus and it converts TDM frames to/from E1/T1
frames.
The HDLC data are sent/received to/from the TDM bus and the framer is used to
get information about the E1/T1 line such as link up/down.

I can update the description to:
--- 8< ---
phandle to the framer node. The framer is in charge of an E1/T1 line
interface connected to the TDM bus. It can be used to get the E1/T1 line
status such as link up/down.
--- 8< ---

Is that better ?

> 
> > +
> > +required:
> > +  - compatible
> > +  - fsl,qmc-chan
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    hdlc {
> > +        compatible = "fsl,qmc-hdlc";
> > +        fsl,qmc-chan = <&qmc 16>;  
> 
> Where does this node live?
> 
> QMC is this[1]? Why don't you just add the compatible to channel@10 in 
> the QMC node?

Indeed, I will move the properties (compatible and framer phandle) to the
QMC channel node.

> 
> Rob
> 
> [1] Documentation/devicetree/bindings/soc/fsl/cpm_qe/fsl,cpm1-scc-qmc.yaml

Best regards,
Hervé

-- 
Hervé Codina, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com