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

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Message-ID: <e6cd13b5-2f7a-4ab1-899c-5867bc0ea64f@kernel.org>
Date: Fri, 18 Oct 2024 17:31:45 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: neil.armstrong@...aro.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 14:31, Neil Armstrong wrote:
> 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.

So I assume this is not linear mapping (simple offset)? If so, this fits
the binding header with identifiers, but I have impression these were
not really used in earlier versions of this patchset. Instead some offsets:
https://lore.kernel.org/all/20241014-a4_pinctrl-v2-1-3e74a65c285e@amlogic.com/

and pre-proccessor.

These looked almost good:
https://lore.kernel.org/all/20240613170816.GA2020944-robh@kernel.org/

but then 0 -> 0
1 -> 1
so where is this need for IDs?

See also last comment from Rob in above email.

Best regards,
Krzysztof