Message-ID: <2bbc2031-89d7-42e9-828e-068fa06eabf4@linaro.org>
Date:   Wed, 22 Nov 2023 16:04:17 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     neil.armstrong@...aro.org, Rob Herring <robh@...nel.org>,
        JunYi Zhao <junyi.zhao@...ogic.com>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Kevin Hilman <khilman@...libre.com>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-amlogic@...ts.infradead.org,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Subject: Re: [PATCH v2 2/6] dt-bindings: pwm: amlogic: add new compatible for
 meson8 pwm type

On 22/11/2023 15:34, Jerome Brunet wrote:
> 
> On Wed 22 Nov 2023 at 09:37, Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
> 
>> On 20/11/2023 11:04, Jerome Brunet wrote:
>>>>>>>>    .../devicetree/bindings/pwm/pwm-amlogic.yaml  | 36 +++++++++++++++++--
>>>>>>>>    1 file changed, 34 insertions(+), 2 deletions(-)
>>>>>>>>
>>>>>>> Reviewed-by: Rob Herring <robh@...nel.org>
>>>>>>>
>>>>>>
>>>>>> I'm puzzled, isn't it recommended to have a per-soc compatible now ?
>>
>> Yes, it is.
>>
>>>>> I have specifically addressed this matter in the description,
>>>>> haven't I ? What good would it do in this case ?
>>
>> There is nothing about compatible naming in commit msg.
> 
> Krzysztof, the whole commit desciption is explanation about why a new
> compatible is introduced. I don't understand this comment.
> 
>>
>>>>
>>>> Yes you did but I was asked for the last year+ that all new compatible
>>>> should be soc specific (while imprecise, in our care soc family should be ok),
>>>> with a possible semi-generic callback with an IP version or a first soc
>>>> implementing the IP.
>>>>
>>>>> Plus the definition of a SoC is very vague. One could argue that
>>>>> the content of the list bellow are vaguely defined families. Should we
>>>>> add meson8b, gxl, gxm, sm1 ? ... or even the actual SoC reference ?
>>>>> This list gets huge for no reason.
>>>>
>>>> I think in our case soc family is reasonable since they share same silicon
>>>> design.
>>>>
>>>>> We know all existing PWM of this type are the same. We have been using
>>>>> them for years. It is not a new support we know nothing about.
>>>>>
>>>>>>
>>>>>> I thought something like:
>>>>>> - items:
>>>>>>      - enum:
>>>>>>          - amlogic,gxbb-pwm
>>>>>>          - amlogic,axg-pwm
>>>>>>          - amlogic,g12a-pwm
>>>>>>      - const: amlogic,pwm-v1
>>>>> I'm not sure I understand what you are suggesting here.
>>>>> Adding a "amlogic,pwm-v1" for the obsolete compatible ? No amlogic DT
>>>>> has that and I'm working to remove this type, so I don't get the point.
>>>>>
>>>>>>
>>>>>> should be preferred instead of a single amlogic,meson8-pwm-v2 ?
>>>>> This is named after the first SoC supporting the type.
>>>>> Naming it amlogic,pwm-v2 would feel weird with the s4 coming after.
>>>>> Plus the doc specifically advise against this type of names.
>>>>
>>>> The -v2 refers to a pure software/dt implementation versioning and not
>>>> an HW version, so I'm puzzled and I requires DT maintainers advice here.
>>>>
>>>> Yes meson8b is the first "known" platform, even if I'm pretty sure meson6 has
>>
>> Yes, this should be SoC-based compatible, unless you have clear
>> versioning scheme by SoC/IP block vendor. You named it not a HW version,
>> which kind of answers to the "unless" case - that's not hardware version.
>>
> 
> This is specifically the point of the comment in commit description.
> We know all the PWMs compatible are the same HW (version) as one found
> in the meson8b.
> 
> It is certain that adding more compatible, listing all the SoC, will be
> useless. I can do it if you insist.

The docs you references insist on that, so yeah, I insist as well.

> 
>>>
>>> This is not my point. I picked this name because I have to pick a
>>> specific device based one. Not because it is actually the first or
>>> not. I don't see a problem with meson6 being compatible with
>>> meson8-pwm-v2, if that ever comes along.
>>
>> No, the point is not to use "v2". Use SoC compatibles.
> 
> It is a SoC compatible. The second one.

"v2" is not the soc. I assume meson8 is one specific SoC, right? Because
elinux says it is a *family*:
https://elinux.org/Amlogic/SoCs


> 
> The first one, as explained in the description was describing the driver
> more that the HW.
> 
> Changing the way clock are passed from DT to the driver would be break
> user of the old compatible. So a new compatible is introduced. I believe
> this is recommended way to introduce incompatible binding changes.

The way is not to introduce incompatible changes. Your way is also not
good as it breaks other users of DTS.

> 
> v2 here denote a new interface version, nothing to do with HW
> versioning. I happy to pick something else to denote this.

Sorry, then it is not a SoC-based compatible.

> 
>>
>>>
>>> I think the binding here satisfy the rule that it should be specific,
>>> and the intent that goes with it:
>>>
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/writing-bindings.rst?h=v6.7-rc2#n42
>>>
>>>> the same pwm architecture, this is why "amlogic,pwm-v1" as fallback seems more
>>>> reasonable and s4 and later pwm could use the "amlogic,pwm-v2"
>>>> fallback.
>>>
>>> That is not how understand this:
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/writing-bindings.rst?h=v6.7-rc2#n82
>>>
>>
>> Again, where the "v2" is defined? Where is any document explaining the
>> mapping between version blocks and SoC parts? Why do you list here only
>> major version? Blocks almost always have also minor (e.g. v2.0).
> 
> Again, v2 does has nothing to do with the HW. Never wrote it was.
> The HW remains the same.

Don't add compatibles which are not related to HW, but represent
software versioning. Software does not matter for the bindings.

That's a clear NAK.

Best regards,
Krzysztof

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