linux-kernel - Re: [PATCH v3 5/9] ARM: dts: stm32: add Hardware debug port (HDP) on stm32mp13

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Message-ID: <f1a63830-0533-4f1c-9116-32e8c1e61a8b@kernel.org>
Date: Wed, 11 Jun 2025 17:48:20 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: 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>,
 Alexandre Torgue <alexandre.torgue@...s.st.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 v3 5/9] ARM: dts: stm32: add Hardware debug port (HDP) on
 stm32mp13

On 11/06/2025 16:08, Clement LE GOFFIC wrote:
> On 6/11/25 08:35, Krzysztof Kozlowski wrote:
>> On 10/06/2025 15:33, Clement LE GOFFIC wrote:
>>> On 6/10/25 14:38, Krzysztof Kozlowski wrote:
>>>> On 10/06/2025 14:02, Clement LE GOFFIC wrote:
>>>>> On 5/29/25 11:01, Krzysztof Kozlowski wrote:
>>>>>> On 28/05/2025 14:14, Clement LE GOFFIC wrote:
>>>>>>>>
>>>>>>>>> +		};
>>>>>>>>> +
>>>>>>>>> +		hdp: pinctrl@...2a000 {
>>>>>>>>> +			compatible = "st,stm32mp131-hdp";
>>>>>>>>> +			reg = <0x5002a000 0x400>;
>>>>>>>>> +			clocks = <&rcc HDP>;
>>>>>>>>>      			status = "disabled";
>>>>>>>>
>>>>>>>> Why are you disabling it? What is missing?
>>>>>>>
>>>>>>> Nothing is missing just disabled by default.
>>>>>>> The node is then enabled when needed in board's dts file.
>>>>>> Nodes should not be disabled by default if they are complete. That's why
>>>>>> I asked what is missing. Drop.
>>>>>
>>>>> Hi Krzysztof, OK I better understand now.
>>>>> So yes the 'pinctrl-*' properties which are board dependent are lacking.
>>>>
>>>> These are not properties of this node.
>>>
>>> Does this mean I should add 'pinctrl-*' properties in bindings yaml file ?
>>> I don't get it..
>>
>> These properties have no meaning here, so the hardware description is
>> complete. You claim that you miss them thus device is incomplete is just
>> not correct: these properties do not belong here! They belong to the
>> board but even there they are totally optional. Why would they be a
>> required resource?
>>
>> To remind: we talk here ONLY about required resources.
> 
> Yes, 'pinctrl-*' properties belongs to the board and are not required.
> So nothing is missing.
> 
> This hdp node in the SoC dtsi file can be enabled by default.
> But the hdp driver will probe and do nothing because without the 
> 'pinctrl-*' properties from the board files it would not be able to 
> access to any pin.


Pinctrl has other features in general, including interfaces to userspace
(as pretty often combined with gpio, although not sure if relevant here).

> I consider enabling this driver by default in SoC dtsi file as just 
> increasing the boot time on "every" board.
> It's the board dts that requires the hdp and provides the 'pinctrl-*' 
> properties to connect the hdp to some SoC pin and then to some signal on 
> the board. For me it's natural to have the status okay only in the board 
> dts file.

The DTS is not the way to optimize boot processes. It is OS-independent
hardware description. My BSD system for example uses smart driver which
avoids probing, but also my user-space needs this device to talk over
exposed interface, so why choice of Linux probing should affect others?

Best regards,
Krzysztof