linux-kernel - Re: [PATCH 1/8] dt-bindings: mfd: stm32-lptimer: add support for stm32mp25

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Message-ID: <8b42f0ad-2993-43b8-9055-6d74dc3bafbe@kernel.org>
Date: Wed, 26 Feb 2025 08:51:19 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Fabrice Gasnier <fabrice.gasnier@...s.st.com>
Cc: lee@...nel.org, ukleinek@...nel.org, alexandre.torgue@...s.st.com,
 robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, wbg@...nel.org,
 jic23@...nel.org, daniel.lezcano@...aro.org, tglx@...utronix.de,
 catalin.marinas@....com, will@...nel.org, devicetree@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-iio@...r.kernel.org, linux-pwm@...r.kernel.org,
 olivier.moysan@...s.st.com
Subject: Re: [PATCH 1/8] dt-bindings: mfd: stm32-lptimer: add support for
 stm32mp25

On 25/02/2025 15:57, Fabrice Gasnier wrote:
> On 2/25/25 13:02, Krzysztof Kozlowski wrote:
>> On Mon, Feb 24, 2025 at 07:01:43PM +0100, Fabrice Gasnier wrote:
>>>    pwm:
>>>      type: object
>>>      additionalProperties: false
>>>  
>>>      properties:
>>>        compatible:
>>> -        const: st,stm32-pwm-lp
>>> +        enum:
>>> +          - st,stm32-pwm-lp
>>> +          - st,stm32mp25-pwm-lp
>>>  
>>>        "#pwm-cells":
>>>          const: 3
>>> @@ -69,7 +76,9 @@ properties:
>>>  
>>>      properties:
>>>        compatible:
>>> -        const: st,stm32-lptimer-counter
>>> +        enum:
>>> +          - st,stm32-lptimer-counter
>>> +          - st,stm32mp25-lptimer-counter
>>
>> Driver changes suggest many of these are compatible. Why isn't this expressed?
> 
> Hi Krzysztof,
> 
> The Low Power Timer (LPTIM) hardware isn't fully backward compatible.
> 
> At driver level, as indicated in the cover-letter, same feature list as
> on STM32MP1x is supported currently. This is probably what makes it look
> like it's compatible, but it's not fully compatible.

I don't understand. Same feature list is supported means fully
compatible, but you say not fully compatible. You are aware that
compatible means not the same?

> 
> The hardware controller is a bit different. Some registers/bits has been
> revisited among other things. This is the purpose for these new compatibles.

We do not discuss new compatibles. We discuss lack of compatibility. If
registers/bits are changed, how existing driver can work with same ID table?



Best regards,
Krzysztof