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

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Message-ID: <adbf1347-b81b-ee5b-f016-109d25b09f81@broadcom.com>
Date:   Tue, 10 Jan 2023 17:08:47 -0800
From:   William Zhang <william.zhang@...adcom.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        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 01/10/2023 02:18 PM, 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";
> 
> in which case, having a fallback compatible on the SoC family that sees 
> this IP being deployed is very useful for client programs of the DT 
> (u-boot or kernel). As long as the fallback works, we use it, the day it 
> stops and a quirk needs to be applied because SoC XYZ has a bug, match 
> the SoC XYZ compatible string.
> 
> FWIW, and feel free to rant at me, we have adopted this convention a 
> while ago for STB chips whereby we want bindings to be defined with:
> 
> <chip specific compatible>, <version of the IP>, <fallback>
> 
> and the fallback may, or may not be matched, but defining in does not 
> hurt at all, in fact it dramatically helps with the boot loader looking 
> for specific nodes because it can search for the fallback.
> 
> If the version specific compatible is not available, it does not get used.

Thanks Florian for jumping in! I was thinking to propose something with 
version info:
    brcm,bcmbca-hsspi-v1.0
    brcm,bcmbca-hsspi-v1.1

To meet STB chip convention, then it would be:
compatible = "brcm,bcm63138-hsspi", "brcm,bcmbca-hsspi-v1.0", 
"brcm,bcmbca-hsspi";
compatible = "brcm,bcm6756-hsspi", "brcm,bcmbca-hsspi-v1.1", 
"brcm,bcmbca-hsspi";

Although I am not a fan of having a chip specific compatible while we 
already have IP version,  I am okay to have it to be consistent with 
Broadcom convention. We will need to remember to update this yaml file 
whenever we have a new chip.

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