netdev - Re: [PATCH 1/3] dt-bings: net: fsl,fec: update compatible item

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Message-ID: <20220818135727.GG149610@dragon>
Date:   Thu, 18 Aug 2022 21:57:27 +0800
From:   Shawn Guo <shawnguo@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Wei Fang <wei.fang@....com>, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        s.hauer@...gutronix.de, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...gutronix.de, festevam@...il.com, linux-imx@....com,
        peng.fan@....com, ping.bai@....com, sudeep.holla@....com,
        linux-arm-kernel@...ts.infradead.org, aisheng.dong@....com
Subject: Re: [PATCH 1/3] dt-bings: net: fsl,fec: update compatible item

On Thu, Aug 18, 2022 at 12:46:33PM +0300, Krzysztof Kozlowski wrote:
> On 18/08/2022 12:22, Shawn Guo wrote:
> > On Thu, Aug 18, 2022 at 10:51:02AM +0300, Krzysztof Kozlowski wrote:
> >> On 18/08/2022 04:33, Shawn Guo wrote:
> >>> On Mon, Jul 04, 2022 at 11:12:09AM +0200, Krzysztof Kozlowski wrote:
> >>>>> diff --git a/Documentation/devicetree/bindings/net/fsl,fec.yaml b/Documentation/devicetree/bindings/net/fsl,fec.yaml
> >>>>> index daa2f79a294f..6642c246951b 100644
> >>>>> --- a/Documentation/devicetree/bindings/net/fsl,fec.yaml
> >>>>> +++ b/Documentation/devicetree/bindings/net/fsl,fec.yaml
> >>>>> @@ -40,6 +40,10 @@ properties:
> >>>>>            - enum:
> >>>>>                - fsl,imx7d-fec
> >>>>>            - const: fsl,imx6sx-fec
> >>>>> +      - items:
> >>>>> +          - enum:
> >>>>> +              - fsl,imx8ulp-fec
> >>>>> +          - const: fsl,imx6ul-fec
> >>>>
> >>>> This is wrong.  fsl,imx6ul-fec has to be followed by fsl,imx6q-fec. I
> >>>> think someone made similar mistakes earlier so this is a mess.
> >>>
> >>> Hmm, not sure I follow this.  Supposing we want to have the following
> >>> compatible for i.MX8ULP FEC, why do we have to have "fsl,imx6q-fec"
> >>> here?
> >>>
> >>> 	fec: ethernet@...50000 {
> >>> 		compatible = "fsl,imx8ulp-fec", "fsl,imx6ul-fec";
> >>> 		...
> >>> 	};
> >>
> >> Because a bit earlier this bindings is saying that fsl,imx6ul-fec must
> >> be followed by fsl,imx6q-fec.
> > 
> > The FEC driver OF match table suggests that fsl,imx6ul-fec and fsl,imx6q-fec
> > are not really compatible.
> > 
> > static const struct of_device_id fec_dt_ids[] = {
> >         { .compatible = "fsl,imx25-fec", .data = &fec_devtype[IMX25_FEC], },
> >         { .compatible = "fsl,imx27-fec", .data = &fec_devtype[IMX27_FEC], },
> >         { .compatible = "fsl,imx28-fec", .data = &fec_devtype[IMX28_FEC], },
> >         { .compatible = "fsl,imx6q-fec", .data = &fec_devtype[IMX6Q_FEC], },
> >         { .compatible = "fsl,mvf600-fec", .data = &fec_devtype[MVF600_FEC], },
> >         { .compatible = "fsl,imx6sx-fec", .data = &fec_devtype[IMX6SX_FEC], },
> >         { .compatible = "fsl,imx6ul-fec", .data = &fec_devtype[IMX6UL_FEC], },
> 
> I don't see here any incompatibility. Binding driver with different
> driver data is not a proof of incompatible devices.

To me, different driver data is a good sign of incompatibility.  It
mostly means that software needs to program the hardware block
differently.


> Additionally, the
> binding describes the hardware, not the driver.
> 
> >         { .compatible = "fsl,imx8mq-fec", .data = &fec_devtype[IMX8MQ_FEC], },
> >         { .compatible = "fsl,imx8qm-fec", .data = &fec_devtype[IMX8QM_FEC], },
> >         { /* sentinel */ }
> > };
> > MODULE_DEVICE_TABLE(of, fec_dt_ids);
> > 
> > Should we fix the binding doc?
> 
> Maybe, I don't know. The binding describes the hardware, so based on it
> the devices are compatible. Changing this, except ABI impact, would be
> possible with proper reason, but not based on Linux driver code.

Well, if Linux driver code is written in the way that hardware requires,
I guess that's just based on hardware characteristics.

To me, having a device compatible to two devices that require different
programming model is unnecessary and confusing.

Shawn