linux-kernel - Re: [PATCH v2 5/6] arm: dts: amlogic: migrate pwms to new meson8 v2 binding

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Date:   Wed, 22 Nov 2023 16:10:03 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Kevin Hilman <khilman@...libre.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-amlogic@...ts.infradead.org, linux-pwm@...r.kernel.org,
        JunYi Zhao <junyi.zhao@...ogic.com>
Subject: Re: [PATCH v2 5/6] arm: dts: amlogic: migrate pwms to new meson8 v2
 binding

On 22/11/2023 15:52, Jerome Brunet wrote:
> 
> On Wed 22 Nov 2023 at 09:39, Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
> 
>> On 17/11/2023 13:59, Jerome Brunet wrote:
>>> Update Amlogic based SoC PWMs to meson8-pwm-v2 compatible
>>
>> Why? Your commit msg must explain this. You break users of this DTS on
>> older kernels and also this makes it impossible to apply via different
>> branches in the same cycle. All this needs explanation and proper
>> justification. Your message tells here nothing, because "what" is quite
>> obvious.
>>
> 
> I provided all the explanation possible through the different commits of
> this series. I can re-state here if it helps

DTS commits stand on their own and must not go via same branch as
driver, so how does driver commit msg help Git history?

> 
>>>
>>> Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
>>> ---
>>>  arch/arm/boot/dts/amlogic/meson.dtsi           |  4 ++--
>>>  arch/arm/boot/dts/amlogic/meson8.dtsi          | 16 +++++++++++++---
>>>  arch/arm/boot/dts/amlogic/meson8b-ec100.dts    |  2 --
>>>  arch/arm/boot/dts/amlogic/meson8b-mxq.dts      |  2 --
>>>  arch/arm/boot/dts/amlogic/meson8b-odroidc1.dts |  2 --
>>>  arch/arm/boot/dts/amlogic/meson8b.dtsi         | 16 +++++++++++++---
>>>  6 files changed, 28 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/arch/arm/boot/dts/amlogic/meson.dtsi b/arch/arm/boot/dts/amlogic/meson.dtsi
>>> index 8e3860d5d916..80cc004ad5fe 100644
>>> --- a/arch/arm/boot/dts/amlogic/meson.dtsi
>>> +++ b/arch/arm/boot/dts/amlogic/meson.dtsi
>>> @@ -83,14 +83,14 @@ i2c_A: i2c@...0 {
>>>  			};
>>>  
>>>  			pwm_ab: pwm@...0 {
>>> -				compatible = "amlogic,meson-pwm";
>>> +				compatible = "amlogic,meson8-pwm-v2";
>>
>> That's breaking users of this DTS (old kernel, out of tree, other
>> projects) for no real reasons without explanation.
> 
> "amlogic,meson-pwm" will continue to match, meaning of bindings is unchanged

No, because new DTS does not have amlogic,meson-pwm, thus all existing
users see breakage.

> 
> How do you propose to fix badly designed bindings then ?

Justify and introduce incompatible changes, breaking the ABI. Anyway
this is a requirement, because, as I said in other reply, you cannot
have compatible for software model!

> 
> if we cant even introduce a new compatible to fix things up. It is supposed to
> stay and broken till the end of time ?

No, you cannot introduce new compatible for new OS.

Fix the bindings instead with proper justification. We did it many
times, what's the problem here?

Best regards,
Krzysztof