linux-kernel - Re: [PATCH V2 4/6] dt-bindings: timestamp: Add Tegra234 support

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Message-ID: <d80001de-3cf7-59e9-5ae7-d8dfe0a1c21e@kernel.org>
Date:   Fri, 10 Mar 2023 19:08:00 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Dipen Patel <dipenp@...dia.com>, thierry.reding@...il.com,
        jonathanh@...dia.com, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-gpio@...r.kernel.org,
        linus.walleij@...aro.org, devicetree@...r.kernel.org,
        linux-doc@...r.kernel.org, robh+dt@...nel.org,
        timestamp@...ts.linux.dev
Subject: Re: [PATCH V2 4/6] dt-bindings: timestamp: Add Tegra234 support

On 10/03/2023 18:19, Dipen Patel wrote:
> On 3/10/23 12:45 AM, Krzysztof Kozlowski wrote:
>> On 09/03/2023 19:49, Dipen Patel wrote:
>>> On 3/8/23 10:16 PM, Krzysztof Kozlowski wrote:
>>>> On 08/03/2023 21:09, Dipen Patel wrote:
>>>>> On 3/8/23 11:05 AM, Krzysztof Kozlowski wrote:
>>>>>> On 08/03/2023 19:45, Dipen Patel wrote:
>>>>>>> On 2/16/23 6:17 AM, Krzysztof Kozlowski wrote:
>>>>>>>> On 14/02/2023 12:55, Dipen Patel wrote:
>>>>>>>>> Added timestamp provider support for the Tegra234 in devicetree
>>>>>>>>> bindings.
>>>>>>>>
>>>>>>>> 1. Your commit does much more. You need to explain it why you drop some
>>>>>>>> property.
>>>>>>> ACK, will address it next patch
>>>>>>>>
>>>>>>>> 2. Bindings go before its usage (in the patchset).
>>>>>>> Ack...
>>>>>>>>
>>>>>>>> 3. Please use scripts/get_maintainers.pl to get a list of necessary
>>>>>>>> people and lists to CC.  It might happen, that command when run on an
>>>>>>>> older kernel, gives you outdated entries.  Therefore please be sure you
>>>>>>>> base your patches on recent Linux kernel.
>>>>>>> It is based on recent linux at the time patch series was sent...
>>>>>>
>>>>>> That's good but then why you do not use scripts/get_maintainers.pl? The
>>>>>> hint about recent kernel was just a hint... Just do not invent addresses
>>>>>> by yourself and use the tool to get them right.
>>>>>>
>>>>> I will take a note for the next patch series to add any missing people. The current
>>>>> list of people/group is what historically helped review this new timestamp/hte subsystem.
>>>>>
>>>>>> (...)
>>>>>>
>>>>>>>>> +  properties:
>>>>>>>>> +    compatible:
>>>>>>>>> +      contains:
>>>>>>>>> +        enum:
>>>>>>>>> +          - nvidia,tegra194-gte-aon
>>>>>>>>
>>>>>>>> This is an ABI break. Does your driver handle it?
>>>>>>> yes, handling patch is part of this patch series.
>>>>>>
>>>>>> Can you point me to the code which does it? I see "return -ENODEV;", so
>>>>>> I think you do not handle ABI break. I could miss something but since
>>>>>> you disagree with me, please at least bring some arguments...
>>>>> Refer to patch https://patchwork.kernel.org/project/timestamp/patch/20230214115553.10416-3-dipenp@nvidia.com/
>>>>> which has compatible properties added and also code changes to reflect addition/deletion of some
>>>>> properties.
>>>>
>>>> I referred to the code which breaks the ABI.
>>>>
>>>>>
>>>>> I am not sure I have understood about ABI break comment. How else one should handle if
>>>>> there is no related gpio controller property found?
>>>>
>>>> In a way it does not break existing users? There are many ways to handle
>>>> it, but I don't know your code to point you.
>>>
>>> It is new subsystem and has only one driver which uses it so far. 
>>
>> We do not talk about subsystem, but Tegra SoC, which is not new. Unless
>> you meant this is new SoC/DTS?
>>
>>> This was a decision taken
>>> after review comments (By Thierry, also in the mailing list) to add this property (nvidia,gpio-controller)
>>> and necessary changes have been made to existing user. From now on, it has to follow this change.
>>
>> What is "it" which has to follow? There are rules for stable ABI and
>> commit msg does not explain why they should not be followed.
> 
> "It" here means hte-tegra194.c HTE provider which is the only one and not being used by any entity
> yet.
> 
>>
>>>
>>>>
>>>>> I am assuming you are referring to the
>>>>> below code from the patch 2 (link above) when you said "return -ENODEV".
>>>>
>>>>
>>>> Your bindings patch points to ABI break without any
>>>> explanation/justification. Then your code #2 patch actually breaks it,
>>>> also without any justification.
>>> I am going to add explanation/justification in the commit message in the next patch series. But to give
>>> you context, discussion happened here https://patchwork.ozlabs.org/project/linux-gpio/patch/20221103174523.29592-3-dipenp@nvidia.com/
>>
>> Either too many messages (and I missed something) or I could not find
>> why ABI break is accepted and justified.
> 
> https://patchwork.ozlabs.org/project/linux-gpio/patch/20221103174523.29592-5-dipenp@nvidia.com/#3000908 and
> affected code/comment at https://patchwork.ozlabs.org/project/linux-gpio/patch/20221103174523.29592-5-dipenp@nvidia.com/#3000908.
> 
> Will it help if I send new patch series with detailed commit message?

Yes. If the binding is not used, it's a perfectly valid reason and
should be mentioned in commit msg.

Best regards,
Krzysztof