linux-kernel - Re: [PATCH 7/9] ARM: dts: stm32: add Hardware debug port (HDP) on stm32mp25

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Message-ID: <df74157e-d141-4045-a244-3168c58c0ff4@foss.st.com>
Date: Thu, 27 Feb 2025 13:16:42 +0100
From: Alexandre TORGUE <alexandre.torgue@...s.st.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        Clement LE GOFFIC
	<clement.legoffic@...s.st.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob
 Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor
 Dooley <conor+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Bartosz Golaszewski <brgl@...ev.pl>
CC: <linux-kernel@...r.kernel.org>, <linux-gpio@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 7/9] ARM: dts: stm32: add Hardware debug port (HDP) on
 stm32mp25



On 2/26/25 22:31, Krzysztof Kozlowski wrote:
> On 26/02/2025 22:26, Krzysztof Kozlowski wrote:
>> On 26/02/2025 16:30, Alexandre TORGUE wrote:
>>>
>>>
>>> On 2/26/25 16:08, Krzysztof Kozlowski wrote:
>>>> On 26/02/2025 10:33, Alexandre TORGUE wrote:
>>>>>>>>> +		hdp: pinctrl@...90000 {
>>>>>>>>> +			compatible = "st,stm32mp-hdp";
>>>>>>>>
>>>>>>>> So here again - you have stm32mp251 SoC, but use entirely different
>>>>>>>> compatible.
>>>>>>>
>>>>>>> Ok so I will use "st,stm32mp15-hdp"
>>>>>>
>>>>>>
>>>>>> This means this is stm32mp15 SoC. I do not see such SoC on list of your
>>>>>> SoCs in bindings. What's more, there are no bindings for other SoC
>>>>>> components for stm32mp15!
>>>>>
>>>>> Yes stm32mp15 is not a "real SoC". I agree that at the beginning of the
>>>>> STM32 story we didn't have a clear rule/view to correctly naming our
>>>>> compatible. We tried to improve the situation to avoid compatible like
>>>>> "st,stm32", "st,stm32mp" or "st,stm32mp1". So we introduced
>>>>> "st,stm32mp13", "st,stm32mp15" or "st,stm32mp25" for new drivers. So yes
>>>>> it represents a SoC family and not a real SoC. We haven't had much
>>>>> negative feedback it.
>>>>>
>>>>> But, if it's not clean to do it in this way, lets define SoC compatible
>>>>> for any new driver.
>>>>
>>>> Compatibles are for hardware.
>>>>
>>>>> For the HDP case it is: "st,stm32mp157" and used for STM32MP13,
>>>>> STM32MP15 end STM32MP25 SoC families (if driver is the same for all
>>>>> those SoCs).
>>>>
>>>> No, it's three compatibles, because you have three SoCs. BTW, writing
>>>> bindings (and online resources and previous reviews and my talks) are
>>>> saying that, so we do not ask for anything new here, anything different.
>>>> At least not new when looking at last 5 years, because 10 years ago many
>>>> rules were relaxed...
>>>
>>> So adding 3 times the same IP in 3 different SoCs implies to have 3
>>
>> Yes. Always, as requested by writing bindings.
>>
>>> different compatibles. So each time we use this same IP in a new SoC, we
>>> have to add a new compatible. My (wrong) understanding was: as we have
>>
>> Yes, as requested by writing bindings and followed up by all recent
>> platforms having decent/active upstream support. See qcom, nxp, renesas
>> for example.
>>
>>> the same IP (same hardware) in each SoC we have the same compatible (and
>>
>> You do not have same hardware. You have same IP, or almost same because
>> they are almost never same, implemented in different hardware.
>>
>>> IP integration differences (clocks, interrupts) are handled by DT
>>> properties.
>>
>> Which binding doc/guide suggested such way? Countless reviews from DT
>> maintainers were saying opposite.
> I was not precise: IP integration differences are of course handles as
> DT properties, but I wanted to say that it does not solve the problem
> that IP integration means you might have differences in this device and
> you should have different quirks.

Yes I agree. We'll take care of it for future development. Maybe, It 
would be nice to apply this rule in our current drivers/DT already 
upstream ?

> 
> And the example in this patchset: entirely different pin functions is a
> proof. This device behaves/operates/integrates differently, thus
> different compatible.

Yes, discussing with Clement, it is clear that we need 3 different 
compatibles.

> Best regards,
> Krzysztof