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

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Message-ID: <4010c7b7-f285-40e6-a032-055c4252ecb7@foss.st.com>
Date: Wed, 26 Feb 2025 19:17:24 +0100
From: Fabrice Gasnier <fabrice.gasnier@...s.st.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
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 2/26/25 08:51, Krzysztof Kozlowski wrote:
> 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?

Hi Krzysztof,

To summarize on dt-bindings side, here is my view, following your
comments on per driver basis of the compatible usage.

Let's keep these new compatibles:
- "st,stm32mp25-lptimer-trigger"
- "st,stm32mp25-lptimer-counter"

Both reflect not only LPTimer hardware update, but also specific
interconnect to other hardware blocks throughout all the STM32MP25 SoC.

Other compatible strings may be dropped. Reading the
revision/identification register of the LPTimer should be enough for
compatibility in the related drivers.

I'll update this in next revision of the series.

Thanks for reviewing,
Best Regards,
Fabrice

> 
> 
> 
> Best regards,
> Krzysztof