linux-kernel - Re: [PATCH 02/16] dt-bindings: spi: Add bcmbca-hsspi controller support

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Date:   Thu, 12 Jan 2023 11:50:21 -0800
From:   William Zhang <william.zhang@...adcom.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Linux SPI List <linux-spi@...r.kernel.org>,
        Broadcom Kernel List <bcm-kernel-feedback-list@...adcom.com>
Cc:     anand.gore@...adcom.com, tomer.yacoby@...adcom.com,
        dan.beygelman@...adcom.com, joel.peshkin@...adcom.com,
        jonas.gorski@...il.com, kursad.oney@...adcom.com, dregan@...l.com,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/16] dt-bindings: spi: Add bcmbca-hsspi controller
 support



On 01/12/2023 12:21 AM, Krzysztof Kozlowski wrote:
> 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?
> 
IMHO it is really confusing that we have all the SoCs but have to bind 
to an antique SoC's spi controller compatible and people may think it is 
a mistake or typo when they don't know they are actually the same. I 
know there are usage like that but when we have clear knowledge of the 
IP block with rev info, I think it is much better to have a precise SoC 
model number and a general revision info in the compatible. As you know 
they are many usage of IP rev info in the compatible too. 
brcm,bcm6328-hsspi will stay so it does not break any existing dts 
reference to that.

Anyway if you still does not like this idea, I will drop the rev info 
and you have it your way.

> 
> Best regards,
> Krzysztof
> 

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