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

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Message-ID: <32a464f8-6a4b-6777-9775-f17e990e0c6a@gmail.com>
Date:   Tue, 10 Jan 2023 14:18:23 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        William Zhang <william.zhang@...adcom.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 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.
-- 
Florian