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

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Date:   Wed, 22 Nov 2023 13:00:49 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Théo Lebrun <theo.lebrun@...tlin.com>,
        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

On 22/11/2023 11:46, Théo Lebrun wrote:

>>
>> How ti,j721e-usb can be and cannot be compatible with am64 in the same time?
> 
> The code tells us that there is no difference between ti,j721e-usb &
> ti,am64-usb. And the commit adding the of_device_id entry agrees, see
> 4f30b9d2315f (usb: cdns3: Add support for TI's AM64 SoC, 2021-01-19).
> Here is the entire patch because it is so small:
> 
>    diff --git a/drivers/usb/cdns3/cdns3-ti.c b/drivers/usb/cdns3/cdns3-ti.c
>    index 90e246601537..eccb1c766bba 100644
>    --- a/drivers/usb/cdns3/cdns3-ti.c
>    +++ b/drivers/usb/cdns3/cdns3-ti.c
>    @@ -214,6 +214,7 @@ static int cdns_ti_remove(struct platform_device *pdev)
> 
>     static const struct of_device_id cdns_ti_of_match[] = {
>       { .compatible = "ti,j721e-usb", },
>    +  { .compatible = "ti,am64-usb", },
>       {},
>     };
>     MODULE_DEVICE_TABLE(of, cdns_ti_of_match);
> 
>>> 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?
>>
>> Logic is wrong. Device either is or is not compatible with something. At
>> least usually. We have some exceptions like SMMU for Adreno. Is this the
>> case? Why the device is and is not compatible with some other variant?
> 
> My understanding is this: j721e & am64 are strictly equivalent. On our

Then this should be expressed in the bindings. Currently and in your
patch, you express that they are not compatible.


...

> 
>  - properties:
>    compatible:
>      oneOf:
>        - const: ti,j7200-usb
>        - items:
>            - const: ti,j721e-usb
>            - const: ti,am64-usb
> 
>    J721E & AM64 are compatible, express that & update devicetrees.
> 
> Option one is simpler & doesn't change devicetrees so I'd lean in that
> direction. What's your opinion?


This one should be for am64.

For your j7200, it depends whether the fallback to j721e makes sense,
IOW, if the Linux can use j721e compatible solely to use j7200 device.

Best regards,
Krzysztof