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Date:   Thu, 12 Jan 2023 09:21:22 +0100
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Subject: Re: [PATCH 02/16] dt-bindings: spi: Add bcmbca-hsspi controller
 support
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To:     William Zhang <william.zhang@broadcom.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Linux SPI List <linux-spi@vger.kernel.org>,
        Broadcom Kernel List <bcm-kernel-feedback-list@broadcom.com>
Cc:     anand.gore@broadcom.com, tomer.yacoby@broadcom.com,
        dan.beygelman@broadcom.com, joel.peshkin@broadcom.com,
        jonas.gorski@gmail.com, kursad.oney@broadcom.com, dregan@mail.com,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Mark Brown <broonie@kernel.org>,
        Rob Herring <robh+dt@kernel.org>, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20230106200809.330769-1-william.zhang@broadcom.com>
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 <b529a53b-d00c-063d-a58d-e64b0300605d@linaro.org>
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From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
In-Reply-To: <e99a71b2-0b05-1a53-1c29-3778b49a3b86@broadcom.com>
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On 11/01/2023 19:44, William Zhang wrote:
> 
> 
> On 01/11/2023 10:12 AM, Krzysztof Kozlowski wrote:
>> On 11/01/2023 19:04, William Zhang wrote:
>>>
>>>
>>> On 01/11/2023 01:02 AM, Krzysztof Kozlowski wrote:
>>>> On 10/01/2023 23:18, Florian Fainelli wrote:
>>>>> On 1/10/23 00:40, Krzysztof Kozlowski wrote:
>>>>>>>> No, it is discouraged in such forms. Family or IP block compatibles
>>>>>>>> should be prepended with a specific compatible. There were many issues
>>>>>>>> when people insisted on generic or family compatibles...
>>>>>>>>
>>>>>>>>> Otherwise we will have to have a compatible string with chip model for
>>>>>>>>> each SoC even they share the same IP. We already have more than ten of
>>>>>>>>> SoCs and the list will increase.  I don't see this is a good solution too.
>>>>>>>>
>>>>>>>> You will have to do it anyway even with generic fallback, so I don't get
>>>>>>>> what is here to gain... I also don't get why Broadcom should be here
>>>>>>>> special, different than others. Why it is not a good solution for
>>>>>>>> Broadcom SoCs but it is for others?
>>>>>>>>
>>>>>>> I saw a few other vendors like these qcom ones:
>>>>>>>      qcom,spi-qup.yaml
>>>>>>>          - qcom,spi-qup-v1.1.1 # for 8660, 8960 and 8064
>>>>>>>          - qcom,spi-qup-v2.1.1 # for 8974 and later
>>>>>>>          - qcom,spi-qup-v2.2.1 # for 8974 v2 and later
>>>>>>>      qcom,spi-qup.yaml
>>>>>>>          const: qcom,geni-spi
>>>>>>
>>>>>> IP block version numbers are allowed when there is clear mapping between
>>>>>> version and SoCs using it. This is the case for Qualcomm because there
>>>>>> is such clear mapping documented and available for Qualcomm engineers
>>>>>> and also some of us (although not public).
>>>>>>
>>>>>>> I guess when individual who only has one particular board/chip and is
>>>>>>> not aware of the IP family,  it is understandable to use the chip
>>>>>>> specific compatible string.
>>>>>>
>>>>>> Family of devices is not a versioned IP block.
>>>>>
>>>>> Would it be acceptable to define for instance:
>>>>>
>>>>> - compatible = "brcm,bcm6868-hsspi", "brcm,bcmbca-hsspi";
>>>>
>>>> Yes, this is perfectly valid. Although it does not solve William
>>>> concerns because it requires defining specific compatibles for all of
>>>> the SoCs.
>>>>
>>>> Best regards,
>>>> Krzysztof
>>>>
>>> As I mentioned in another email,  I would be okay to use these
>>> compatibles to differentiate by ip rev and to conforms to brcm convention:
>>> "brcm,bcmXYZ-hsspi", "brcm,bcmbca-hsspi-v1.0", "brcm,bcmbca-hsspi";
>>> "brcm,bcmXYZ-hsspi", "brcm,bcmbca-hsspi-v1.1", "brcm,bcmbca-hsspi";
>>
>>
>> Drop the version in such case, no benefits. I assume XYZ is the SoC
>> model, so for example 6868.
>>
> Yes XYZ is the SoC model
>>>
>>> In the two drivers I included in this series, it will be bound to
>>> brcm,bcmbca-hsspi-v1.0 (in additional to brcm,bcm6328-hsspi) and
>>> brcm,bcmbca-hsspi-v1.1 respectively.  This way we don't need to update
>>> the driver with a new soc specific compatible whenever a new chips comes
>>> out.
>>
>> I don't understand why do you bring it now as an argument. You defined
>> before that your driver will bind to the generic bcmbca compatible, so
>> now it is not enough?
>>
> No as we are adding chip model specific info here.  The existing driver 
> spi-bcm63xx-hsspi.c only binds to brcm,bcm6328-hsspi. This driver 
> supports all the chips with rev1.0 controller so I am using this 6328 
> string for other chips with v1.0 in the dts patch, which is not ideal.

Why? This is perfectly ideal and usual case. Why changing it?

> Now I have to add more compatible to this driver and for each new chip 
> with 1.0 in the future if any.

Why you cannot use compatibility with older chipset?


Best regards,
Krzysztof