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Message-ID: <2196dd29-93ee-00f7-65b4-ede73aa8ba77@linaro.org>
Date:   Wed, 31 May 2023 21:46:45 +0200
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Subject: Re: [PATCH v11 1/2] dt-bindings: spi: add loongson spi
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To:     zhuyinbo <zhuyinbo@loongson.cn>,
        Conor Dooley <conor.dooley@microchip.com>
Cc:     Mark Brown <broonie@kernel.org>, Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        linux-spi@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, Jianmin Lv <lvjianmin@loongson.cn>,
        wanghongliang@loongson.cn, Liu Peibao <liupeibao@loongson.cn>,
        loongson-kernel@lists.loongnix.cn
References: <20230522071030.5193-1-zhuyinbo@loongson.cn>
 <20230522071030.5193-2-zhuyinbo@loongson.cn>
 <20230524-pouncing-variable-c520e85f8db8@wendy>
 <b1e3d199-de5a-f8d5-9159-4965e9e1f5ef@loongson.cn>
 <20230524-relative-trimmer-046fb26a7764@wendy>
 <99b362c2-640c-9150-26ee-e9add4483886@loongson.cn>
From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
In-Reply-To: <99b362c2-640c-9150-26ee-e9add4483886@loongson.cn>
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On 25/05/2023 04:22, zhuyinbo wrote:
> 
> 
> 在 2023/5/24 下午6:29, Conor Dooley 写道:
>> On Wed, May 24, 2023 at 05:44:38PM +0800, zhuyinbo wrote:
>>>
>>>
>>> 在 2023/5/24 下午4:56, Conor Dooley 写道:
>>>> On Mon, May 22, 2023 at 03:10:29PM +0800, Yinbo Zhu wrote:
>>>>> Add the Loongson platform spi binding with DT schema format using
>>>>> json-schema.
>>>>>
>>>>> Signed-off-by: Yinbo Zhu <zhuyinbo@loongson.cn>
>>>>> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
>>>>> ---
>>>>>    .../bindings/spi/loongson,ls2k-spi.yaml       | 41 +++++++++++++++++++
>>>>>    MAINTAINERS                                   |  6 +++
>>>>>    2 files changed, 47 insertions(+)
>>>>>    create mode 100644 Documentation/devicetree/bindings/spi/loongson,ls2k-spi.yaml
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/spi/loongson,ls2k-spi.yaml b/Documentation/devicetree/bindings/spi/loongson,ls2k-spi.yaml
>>>>> new file mode 100644
>>>>> index 000000000000..d0be6e5378d7
>>>>> --- /dev/null
>>>>> +++ b/Documentation/devicetree/bindings/spi/loongson,ls2k-spi.yaml
>>>>> @@ -0,0 +1,41 @@
>>>>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>>>>> +%YAML 1.2
>>>>> +---
>>>>> +$id: http://devicetree.org/schemas/spi/loongson,ls2k-spi.yaml#
>>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>>> +
>>>>> +title: Loongson SPI controller
>>>>> +
>>>>> +maintainers:
>>>>> +  - Yinbo Zhu <zhuyinbo@loongson.cn>
>>>>> +
>>>>> +allOf:
>>>>> +  - $ref: /schemas/spi/spi-controller.yaml#
>>>>> +
>>>>> +properties:
>>>>> +  compatible:
>>>>> +    enum:
>>>>> +      - loongson,ls2k-spi
>>>>
>>>> I am sorry to jump in here at such a late stage with a (potentially)
>>>> trivial question. "ls2k" is the SoC family rather than a specific model
>>>> as far as I understand.
>>>> The answer is probably yes, but do all SoCs in the family have an
>>>> identical version of the IP?
>>>
>>>
>>> No, but the spi supported by this loongson spi driver are all the same
>>> identical version, and other type or verion spi will be supported as
>>> needed in the future.
>>
>> Does having a catch-all compatible make sense then when not all SoCs in
>> the ls2k family will actually be able to use this driver?
> 
> 
> Yes, it is make sense as it can reduce the workload of the community.
> For the Loongson platform, the versions of spi peripherals are almost
> the same, except for a few  or individual SoCs.  And we have also
> discussed compatible internally, and we tend to define it this way.

So you have chosen different path than what's clearly recommended by
community, existing experience and documentation:

https://elixir.bootlin.com/linux/v6.1-rc1/source/Documentation/devicetree/bindings/writing-bindings.rst#L42

Family names are not accepted as specific compatibles. Whenever they
were accepted, it lead to problems. All the time.

https://lore.kernel.org/all/20220822181701.GA89665-robh@kernel.org/
https://lore.kernel.org/all/78651e07-6b3e-4243-8e1f-fcd1dfb3ffe1@www.fastmail.com/
https://lore.kernel.org/all/288f56ba9cfad46354203b7698babe91@walle.cc/
https://lore.kernel.org/all/106e443a-e765-51fe-b556-e4e7e2aa771c@linaro.org/
and many many more discussions.

You should choose carefully, because we will keep NAK-ing adding
properties to circumvent missing compatibles.
> 
>> Or am I misunderstanding and all ls2k SoCs do work with this driver and
>> you were talking about other, future products?
> 
> Actually, in 2k500 has one special type spi was only one cs and their's
> register definition was different from common type spi thus this driver
> doesn't support but this driver can support another common type spi in
> 2k500.  for this special type spi I will add support as needed in the
> future.

Bindings are for hardware, not driver. What does your driver support or
does not, matters less.

Best regards,
Krzysztof