linux-kernel - Re: [PATCH v2 2/6] dt-bindings: pwm: amlogic: add new compatible for meson8 pwm type

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Date:   Mon, 20 Nov 2023 11:04:48 +0100
From:   Jerome Brunet <jbrunet@...libre.com>
To:     neil.armstrong@...aro.org
Cc:     Jerome Brunet <jbrunet@...libre.com>,
        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 Mon 20 Nov 2023 at 10:55, neil.armstrong@...aro.org wrote:

> Hi Jerome,
>
> On 20/11/2023 10:18, Jerome Brunet wrote:
>> On Mon 20 Nov 2023 at 09:27, Neil Armstrong <neil.armstrong@...aro.org>
>> wrote:
>> 
>>> Hi Rob,
>>>
>>> On 19/11/2023 17:05, Rob Herring wrote:
>>>> On Fri, 17 Nov 2023 13:59:12 +0100, Jerome Brunet wrote:
>>>>> Add a new compatible for the pwm found in the meson8 to sm1 Amlogic SoCs.
>>>>>
>>>>> The previous clock bindings for these SoCs described the driver and not the
>>>>> HW itself. The clock provided was used to set the parent of the input clock
>>>>> mux among the possible parents hard-coded in the driver.
>>>>>
>>>>> The new bindings allows to describe the actual clock inputs of the PWM in
>>>>> DT, like most bindings do, instead of relying of hard-coded data.
>>>>>
>>>>> The new bindings make the old one deprecated.
>>>>>
>>>>> There is enough experience on this HW to know that the PWM is exactly the
>>>>> same all the supported SoCs. There is no need for a per-SoC compatible.
>>>>>
>>>>> Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
>>>>> ---
>>>>>    .../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 ?
>> I have specifically addressed this matter in the description,
>> haven't I ? What good would it do in this case ?
>
> 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

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.

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

>
> Neil
>> 
>>>
>>> Neil
>>