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

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Date:   Wed, 13 Jul 2022 11:37:18 -0700
From:   William Zhang <william.zhang@...adcom.com>
To:     Rafał Miłecki <rafal@...ecki.pl>
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

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 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?

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