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

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Message-ID: <2e7a65da-5c1d-4dd4-ac69-7559a53afdf3@linaro.org>
Date:   Mon, 20 Nov 2023 10:55:41 +0100
From:   neil.armstrong@...aro.org
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     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

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
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.

Neil
> 
>>
>> Neil
>