linux-kernel - Re: [PATCH v2 1/7] dt-bindings: usb: ti,j721e-usb: add ti,j7200-usb compatible

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Message-Id: <CX4NADEZZEO1.3TXPVNOONKBCF@tleb-bootlin-xps13-01>
Date:   Tue, 21 Nov 2023 17:53:32 +0100
From:   Théo Lebrun <theo.lebrun@...tlin.com>
To:     "Krzysztof Kozlowski" <krzysztof.kozlowski@...aro.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        "Conor Dooley" <conor+dt@...nel.org>,
        "Roger Quadros" <rogerq@...nel.org>,
        "Peter Chen" <peter.chen@...nel.org>,
        "Pawel Laszczak" <pawell@...ence.com>,
        "Nishanth Menon" <nm@...com>,
        "Vignesh Raghavendra" <vigneshr@...com>,
        "Tero Kristo" <kristo@...nel.org>
Cc:     <linux-usb@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Grégory Clement <gregory.clement@...tlin.com>,
        "Conor Dooley" <conor.dooley@...rochip.com>
Subject: Re: [PATCH v2 1/7] dt-bindings: usb: ti,j721e-usb: add ti,j7200-usb
 compatible

Hello,

On Mon Nov 20, 2023 at 6:32 PM CET, Krzysztof Kozlowski wrote:
> On 20/11/2023 18:06, Théo Lebrun wrote:
> > On this platform, the controller & its wrapper are reset on resume. This
> > makes it have a different behavior from other platforms.
> > 
> > We allow using the new compatible with a fallback onto the original
> > ti,j721e-usb compatible. We therefore allow using an older kernel with
>
> Where is fallback ti,j721e-usb used? Please point me to the code.

No fallback is implemented in code. Using a kernel that doesn't have
this patch series but a more recent devicetree: DT has both
devicetrees & the kernel will know which driver to use.

That is opposed to having only compatible = "ti,j7200-usb". If using an
old kernel, it would not know what driver to match it to.

[...]

> > --- a/Documentation/devicetree/bindings/usb/ti,j721e-usb.yaml
> > +++ b/Documentation/devicetree/bindings/usb/ti,j721e-usb.yaml
> > @@ -12,11 +12,15 @@ maintainers:
> >  properties:
> >    compatible:
> >      oneOf:
> > +      - const: ti,j7200-usb
> >        - const: ti,j721e-usb
> >        - const: ti,am64-usb
> >        - items:
> >            - const: ti,j721e-usb
> >            - const: ti,am64-usb
> > +      - items:
> > +          - const: ti,j721e-usb
>
> This makes little sense. It's already on the list. Twice! Don't add it
> third time.
>
> I am sorry, but this binding makes no sense. I mean, existing binding
> makes no sense, but your change is not making it anyhow better.

The goal of the DT schema pre-patch was to allow all three:

   compatible = "ti,j721e-usb";
   compatible = "ti,am64-usb";
   compatible = "ti,j721e-usb", "ti,am64-usb";

I've followed the same scheme & added both of those:

   compatible = "ti,j7200-usb";
   compatible = "ti,j7200-usb", "ti,j721e-usb";

I messed up the ordering in the added 'items' options, but the logic
seems right to me. And dtbs_check agrees. Am I missing something?

Thanks,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com