Message-ID: <341950d6-1a2c-4191-948a-6e572fa74cc0@foss.st.com>
Date: Thu, 12 Jun 2025 15:28:51 +0200
From: Clement LE GOFFIC <clement.legoffic@...s.st.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        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-gpio@...r.kernel.org>, <linux-stm32@...md-mailman.stormreply.com>,
        <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [Linux-stm32] [PATCH v3 5/9] ARM: dts: stm32: add Hardware debug
 port (HDP) on stm32mp13

On 6/12/25 15:21, Clement LE GOFFIC wrote:
> On 6/12/25 15:09, Krzysztof Kozlowski wrote:
>> On 12/06/2025 15:02, Clement LE GOFFIC wrote:
>>> On 6/12/25 13:05, Krzysztof Kozlowski wrote:
>>>> On 12/06/2025 11:31, Clement LE GOFFIC wrote:
>>>>> On 6/11/25 17:48, Krzysztof Kozlowski wrote:
>>>>>> 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).
>>>>>
>>>>> You're right. Also HDP pinctrl has a GPO feature accessible from 
>>>>> userspace.
>>>>> But by default the HDP is not connected to any pad; it needs the board
>>>>
>>>> OK, then that was the answer to my first question - what is missing.
>>>> However aren't these pads connected internally also to other parts of
>>>> the SoC (like in most other vendors)?
>>>
>>> No, HDP "output pads" are only connected to SoC pinctrl to route outside
>>> the internal SoC signals for debug purpose.
>>>
>>>>> 'pinctrl-*' properties to configure the SoC pinctrl and expose HDP on
>>>>> the SoC pads.
>>>>>
>>>>> That's why for me the enabling of the driver should be in the board 
>>>>> file
>>>>> together with the SoC pinctrl configuration.
>>>>
>>>> And what are the default pad settings configured by HPD driver in
>>>> bootloader (and by bootloader I mean one of few bootloaders this is
>>>> going to be used on like U-Boot)
>>>
>>> The default is to use the GPIO of the SoC pinctrl. The HDP is not routed
>>> outside.
>>>    >>
>>>>> The userland cannot change the pinctrl alternate function mux, this is
>>>>> statically defined by the devicetree.
>>>>
>>>> If you expose GPIO then userland needs this regardless of alternate 
>>>> mux.
>>>> IOW, board level could not configure mux because it should be always
>>>> configured to safe GPIO input.
>>>
>>> For userland sight view, SoC GPIO are preferred instead of HDP.
>>> HDP is only GPO not GPIO. 'pinctrl-*' properties configure at the same
>>> time the SoC pinctrl mux to HDP and the HDP pinctrl mux to one of the
>>> HDP functions (e.g. GPO).
>> Thanks, that's explains, fine to keep it disabled. Unless it is obvious
>> for everyone, it would be nice to put it in commit msg.
> 
> You're welcome, so I'll provide the V6 with more information in the
> commit message of patch [5-7] among other needed fixes.

V5*

>>
>> Best regards,
>> Krzysztof
> 
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