linux-kernel - Re: [RFC PATCH 1/3] dt-bindings: arm64: bcmbca: Merge BCM4908 into BCMBCA

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Date:   Wed, 13 Jul 2022 22:23:07 +0200
From:   Rafał Miłecki <rafal@...ecki.pl>
To:     William Zhang <william.zhang@...adcom.com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Linux ARM List <linux-arm-kernel@...ts.infradead.org>,
        kursad.oney@...adcom.com, anand.gore@...adcom.com,
        dan.beygelman@...adcom.com, f.fainelli@...il.com,
        Broadcom Kernel List <bcm-kernel-feedback-list@...adcom.com>,
        joel.peshkin@...adcom.com,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/3] dt-bindings: arm64: bcmbca: Merge BCM4908 into
 BCMBCA

On 2022-07-13 20:37, William Zhang wrote:
> Hi Rafal,
> 
> On 7/13/22 03:58, Rafał Miłecki wrote:
>> On 2022-07-13 12:50, Rafał Miłecki wrote:
>>> On 2022-07-13 02:57, William Zhang wrote:
>>>> On 7/12/22 11:18, Krzysztof Kozlowski wrote:
>>>>> On 12/07/2022 19:37, William Zhang wrote:
>>>>>>>> +      - description: BCM4908 Family based boards
>>>>>>>> +        items:
>>>>>>>> +          - enum:
>>>>>>>> +              # BCM4908 SoC based boards
>>>>>>>> +              - brcm,bcm94908
>>>>>>>> +              - asus,gt-ac5300
>>>>>>>> +              - netgear,raxe500
>>>>>>>> +              # BCM4906 SoC based boards
>>>>>>>> +              - brcm,bcm94906
>>>>>>>> +              - netgear,r8000p
>>>>>>>> +              - tplink,archer-c2300-v1
>>>>>>>> +          - enum:
>>>>>>>> +              - brcm,bcm4908
>>>>>>>> +              - brcm,bcm4906
>>>>>>>> +              - brcm,bcm49408
>>>>>>> 
>>>>>>> This is wrong.  brcm,bcm94908 followed by brcm,bcm4906 does not 
>>>>>>> look
>>>>>>> like valid list of compatibles.
>>>>>>> 
>>>>>> For 4908 board variant, it will need to be followed by 4908 chip. 
>>>>>> Sorry
>>>>>> for the basic question but is there any requirement to enforce 
>>>>>> this kind
>>>>>> of rule?  I would assume dts writer know what he/she is doing and 
>>>>>> select
>>>>>> the right combination.
>>>>> 
>>>>> The entire point of DT schema is to validate DTS. Combination like 
>>>>> above
>>>>> prevents that goal.
>>>>> 
>>>>> Best regards,
>>>>> Krzysztof
>>>> Understand the DT schema purpose. But items property allows multiple
>>>> enums in the list which gives a lot of flexibility but make it hard 
>>>> to
>>>> validate. I am not familiar with DT schema, is there any directive 
>>>> to
>>>> specify one enum value depending on another so dts validation tool 
>>>> can
>>>> report error if combination is wrong?
>>>> 
>>>> This is our preferred format of all bcmbca compatible string
>>>> especially when we could have more than 10 chip variants for the 
>>>> same
>>>> chip family and we really want to work on the chip family id.  We 
>>>> will
>>>> make sure they are in the right combination in our own patch and 
>>>> patch
>>>> from other contributors. Would this work? If not, I will probably 
>>>> have
>>>> to revert the change of 4908(maybe append brcm,bcmbca as this chip
>>>> belongs to the same bca group) and use "enum board variant", "const
>>>> main chip id", "brcm,bca" for all other chips as our secondary 
>>>> choice.
>>> 
>>> I'm not sure why I didn't even receive 1/3 and half of discussion
>>> e-mails.
>>> 
>>> You can't just put all strings into a single bag and allow mixing 
>>> them
>>> in any combos. Please check how it's properly handled in the current
>>> existing binding:
>>> Documentation/devicetree/bindings/arm/bcm/brcm,bcm4908.yaml
>>> 
>>> Above binding enforces that non-matching compatible strings are not 
>>> used
>>> together.
>> 
>> I just noticed you're actually removing brcm,bcm4908.yaml in the 2/3 
>> so
>> you must be aware of that file.
>> 
>> So you see a cleanly working binding in the brcm,bcm4908.yaml but
>> instead copying it you decided to wrote your own one from scratch.
>> Incorrectly.
>> 
>> This smells of NIH (not invented here). Please just use that binding I
>> wrote and move if it needed.
> 
> Not mean to discredit any of your work and I did copy over your
> binding and combine them into one SoC entry to the new bcmbca.yaml and
> add you as one of the maintainer to this file. As this change would
> certainly concern you, that's why I sent RFC first.  As I explained in
> the cover letter, the purpose of the change is to reduce the number of
> compatible strings and keep one entry for one chip family due to
> possible large number of chip variants.  But since there is no way to
> validate the combination, I will copy the existing 4908 bindings as
> they are now

Right. I believe we need that.


> but I would propose to append "brcm, bcmbca" as it is
> part of bcmbca chip. And for the other chips, we would just use enum
> "board variant", const "main chip id", const "brcm,bca".  Does that
> sound good to you?

Nitpicking: you meant "brcm,bcmbca" (typo) but sounds absolutely fine!