linux-kernel - Re: [PATCH v2 05/28] dt-bindings: net: Add support for QMC HDLC

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Message-ID: <20230727110948.7926a532@bootlin.com>
Date:   Thu, 27 Jul 2023 11:09:48 +0200
From:   Herve Codina <herve.codina@...tlin.com>
To:     Conor Dooley <conor@...nel.org>
Cc:     "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>,
        Rob Herring <robh+dt@...nel.org>,
        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>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        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 v2 05/28] dt-bindings: net: Add support for QMC HDLC

Hi Conor,

On Thu, 27 Jul 2023 09:19:59 +0100
Conor Dooley <conor@...nel.org> wrote:

> On Wed, Jul 26, 2023 at 05:02:01PM +0200, Herve Codina wrote:
> > 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.
> > 
> > Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> > ---
> >  .../devicetree/bindings/net/fsl,qmc-hdlc.yaml | 41 +++++++++++++++++++
> >  1 file changed, 41 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..8bb6f34602d9
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/net/fsl,qmc-hdlc.yaml
> > @@ -0,0 +1,41 @@
> > +# 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: QMC HDLC  
> 
> "QMC HDLC" seems excessively terse.

The name was based on the fsl,qmc-audio.yaml already present upstream.
  https://elixir.bootlin.com/linux/v6.4/source/Documentation/devicetree/bindings/sound/fsl,qmc-audio.yaml

If needed, I can change to:
  title: QMC (QUICC Multichannel Controller) HDLC
Let me known if it is better to you.

> 
> > +
> > +maintainers:
> > +  - Herve Codina <herve.codina@...tlin.com>
> > +
> > +description: |
> > +  The QMC HDLC uses a QMC (QUICC Multichannel Controller) channel to transfer
> > +  HDLC data.
> > +
> > +properties:
> > +  compatible:
> > +    const: fsl,qmc-hdlc
> > +
> > +  fsl,qmc-chan:  
> 
> Perhaps I am just showing my lack of knowledge in this area, but what is
> fsl specific about wanting a reference to the channel of a "QMC"?
> Is this something that hardware from other manufacturers would not also
> want to do?

The QMC and the QMC channel are something specific to the SoC. This IP is only
available on some Freescale/NXP SoCs.

When I upstreamed the 'fsl,qmc-audio.yaml', I first used a generic name for this
property and Kristoff asked to change to a vendor prefixed name.
  https://lore.kernel.org/linux-kernel/1dfade07-f8c4-2e16-00dc-c7d183708259@linaro.org/

Based on this, as the property 'fsl,qmc-chan' has the exact same meaning in
fsl,qmc-audio.yaml and fsl,qmc-hdlc.yaml, I use the same name.

Best regards,
Hervé

> 
> > +    $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.
> > +
> > +required:
> > +  - compatible
> > +  - fsl,qmc-chan
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    hdlc {
> > +        compatible = "fsl,qmc-hdlc";
> > +        fsl,qmc-chan = <&qmc 16>;
> > +    };
> > -- 
> > 2.41.0
> >