linux-kernel - Re: [PATCH v3 1/2] gpio: dt-bindings: add parsing of loongson gpio offset

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Date:   Mon, 14 Aug 2023 21:18:39 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Yinbo Zhu <zhuyinbo@...ngson.cn>,
        Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Conor Dooley <conor@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-gpio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jianmin Lv <lvjianmin@...ngson.cn>, wanghongliang@...ngson.cn,
        loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH v3 1/2] gpio: dt-bindings: add parsing of loongson gpio
 offset

On 14/08/2023 05:39, Yinbo Zhu wrote:
> 
> 
> 在 2023/8/11 下午10:25, Bartosz Golaszewski 写道:
>> On Thu, Aug 10, 2023 at 8:19 AM Yinbo Zhu <zhuyinbo@...ngson.cn> wrote:
>>>
>>>
>>>
>>> 在 2023/8/9 下午11:39, Conor Dooley 写道:
>>>> On Wed, Aug 09, 2023 at 03:47:55PM +0800, Yinbo Zhu wrote:
>>>>> 在 2023/8/8 下午8:05, Conor Dooley 写道:
>>>>>> On Mon, Aug 07, 2023 at 03:40:42PM +0800, Yinbo Zhu wrote:
>>>>
>>>>>>> +  loongson,gpio-ctrl-mode:
>>>>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>>>>>> +    description:
>>>>>>> +      This option indicate this GPIO control mode, where '0' represents
>>>>>>> +      bit control mode and '1' represents byte control mode.
>>>>>>
>>>>>> How is one supposed to know which of these modes to use?
>>>>>
>>>>>
>>>>> Byte mode is to access by byte, such as gpio3, the base address of the
>>>>> gpio controller is offset by 3 bytes as the access address of gpio3.
>>>>>
>>>>> The bit mode is the normal mode that like other platform gpio and it is
>>>>> to access by bit.
>>>>>
>>>>> If both modes are supported, it is recommended to prioritize using byte
>>>>> mode that according to spec.
>>>>
>>>> So, sounds like this property should instead be a boolean that notes
>>>> whether the hardware supports the mode or not, rather than the current
>>>> enum used to determine software policy.
>>>
>>>
>>> okay, I got it, I will use boolean,
>>>
>>
>> Why do you want to put it into device-tree so badly? This is not the
>> first driver that would have of_match_data for different variants
>> where you can have a structure that would keep offsets for different
>> models. It's not like you will have hundreds of "compatible" chips
>> anyway, most likely just a few?
> 
> 
> Using this ways that put offset property into device-tree that can be
> compatible with future GPIO chips without the need to modify drivers,

That's not an argument for putting into DT.

> such as more 2K chips in the future, but use of_match_data and data
> field of_device_id, which every time a new SoC is released, the GPIO
> driver needs to be modified once, which is not friendly to us.

Sorry, "friendly" is again hardly an argument what should or should not
be in DT.

Best regards,
Krzysztof