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

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Message-ID: <c8a03fa6-9ac5-434f-ba13-78e47ad341b8@kernel.org>
Date: Mon, 21 Oct 2024 11:56:42 +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 21/10/2024 09:38, neil.armstrong@...aro.org wrote:
> On 18/10/2024 17:31, Krzysztof Kozlowski wrote:
>> 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?
> 
> ???
> 
> Of courses the first pins maps to linear values...
> 
>>
>> See also last comment from Rob in above email.
> 
> OK so I looked and v2 was in fact correct:
> https://lore.kernel.org/all/20241014-a4_pinctrl-v2-1-3e74a65c285e@amlogic.com/
> 
> ====><=================
> +/* Standard port */
> +#define GPIOB_START	0
> +#define GPIOB_NUM	14
> +
> +#define GPIOD_START	(GPIOB_START + GPIOB_NUM)
> +#define GPIOD_NUM	16
> +
> +#define GPIOE_START	(GPIOD_START + GPIOD_NUM)
> +#define GPIOE_NUM	2
> +
> +#define GPIOT_START	(GPIOE_START + GPIOE_NUM)
> +#define GPIOT_NUM	23
> +
> +#define GPIOX_START	(GPIOT_START + GPIOT_NUM)
> +#define GPIOX_NUM	18
> +
> +#define PERIPHS_PIN_NUM	(GPIOX_START + GPIOX_NUM)
> +
> +/* Aobus port */
> +#define GPIOAO_START	0
> +#define GPIOAO_NUM	7
> +
> +/* It's a special definition, put at the end, just 1 num */
> +#define	GPIO_TEST_N	(GPIOAO_START +  GPIOAO_NUM)
> +#define	AOBUS_PIN_NUM	(GPIO_TEST_N + 1)
> +
> +#define AMLOGIC_GPIO(port, offset)	(port##_START + (offset))
> ====><=================
> 
> is exactly what rob asked for, and you nacked it.

No, this is not what was asked, at least according to my understanding.
Number of GPIOs is not an ABI. Neither is their relationship, where one
starts and other ends.

Maybe I missed something, but I could not find any users of these in the
DTS. Look:

https://lore.kernel.org/all/20241014-a4_pinctrl-v2-3-3e74a65c285e@amlogic.com/

Where is any of above defines?

Maybe they will be visible in the consumer code, but I did not imagine
such use. You expect:
reset-gpios = <&ctrl GPIOAO_START 1>???

How this is anyway close to what we have for Aspeed or Tegra? I
understand that there was no consumer DTS, but you have also cover
letter which could bring some answers in case reviewer is confused. What
did cover letter say? Let me quote:

"Add pinctrl driver support for Amloigc A4 SoC"




Best regards,
Krzysztof