linux-kernel - Re: [PATCH v3 1/3] dt-bindings: pinctrl: Add support for Amlogic A4 SoCs

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Message-ID: <5ad8f396-84a5-486d-b90d-98fbf8882d1b@linaro.org>
Date: Fri, 18 Oct 2024 14:31:56 +0200
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Krzysztof Kozlowski <krzk@...nel.org>,
 Jerome Brunet <jbrunet@...libre.com>, Xianwei Zhao <xianwei.zhao@...ogic.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Kevin Hilman <khilman@...libre.com>,
 Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
 Bartosz Golaszewski <brgl@...ev.pl>, linux-gpio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] dt-bindings: pinctrl: Add support for Amlogic A4
 SoCs

On 18/10/2024 12:13, Krzysztof Kozlowski wrote:
> On 18/10/2024 11:20, Jerome Brunet wrote:
>> On Fri 18 Oct 2024 at 17:01, Xianwei Zhao <xianwei.zhao@...ogic.com> wrote:
>>
>>> Hi Jerome,
>>>     Thanks for your reply.
>>>
>>> On 2024/10/18 16:39, Jerome Brunet wrote:
>>>> [ EXTERNAL EMAIL ]
>>>> On Fri 18 Oct 2024 at 10:28, Krzysztof Kozlowski <krzk@...nel.org> wrote:
>>>>
>>>>> On 18/10/2024 10:10, Xianwei Zhao via B4 Relay wrote:
>>>>>> From: Xianwei Zhao <xianwei.zhao@...ogic.com>
>>>>>>
>>>>>> Add the new compatible name for Amlogic A4 pin controller, and add
>>>>>> a new dt-binding header file which document the detail pin names.
>>>> the change does not do what is described here. At least the description
>>>> needs updating.
>>>>
>>>
>>> Will do.
>>>
>>>> So if the pin definition is now in the driver, does it mean that pins have
>>>> to be referenced in DT directly using the made up numbers that are
>>>> created in pinctrl-amlogic-a4.c at the beginning of patch #2 ?
>>>>
>>>
>>> Yes.
>>>
>>>> If that's case, it does not look very easy a read.
>>>>
>>>
>>> It does happen. The pin definition does not fall under the category of
>>> binding.
>>>
>>> https://lore.kernel.org/all/106f4321-59e8-49b9-bad3-eeb57627c921@amlogic.com/
>>
>> So the expectation is that people will write something like:
>>
>>   reset-gpios = <&gpio 42 GPIO_ACTIVE_LOW>;
>>
>> And others will go in the driver to see that is maps to GPIOX_10 ? the number
>> being completly made up, with no link to anything HW/Datasheet
>> whatsoever ?
>>
>> This is how things should be done now ?
> 
> Why would you need to do this? Why it cannot be <&gpio 10
> GPIO_ACTIVE_LOW>, assuming it is GPIO 10?
> 
> Bindings have absolutely nothing to do with it. You have GPIO 10, not
> 42, right?

There's no 1:1 mapping between the number and the pin on Amlogic platforms,
so either a supplementary gpio phandle cell is needed to encode the gpio pin
group or some bindings header is needed to map those to well known identifiers.

Neil

> 
> Best regards,
> Krzysztof
>