linux-kernel - Re: [PATCH v3 1/3] dt-bindings: interconnect: Remove required reg field

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Date:   Mon, 7 Nov 2022 19:28:36 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Georgi Djakov <djakov@...nel.org>,
        Melody Olvera <quic_molvera@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     Odelu Kukatla <quic_okukatla@...cinc.com>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] dt-bindings: interconnect: Remove required reg
 field

On 07/11/2022 15:36, Georgi Djakov wrote:
> Hi,
> 
> On 2.11.22 23:11, Krzysztof Kozlowski wrote:
>> On 31/10/2022 19:29, Melody Olvera wrote:
>>>
>>>
>>> On 10/27/2022 8:29 AM, Krzysztof Kozlowski wrote:
>>>> On 26/10/2022 15:05, Melody Olvera wrote:
>>>>> Many of the *-virt compatible devices do not have a reg field
>>>>> so remove it as required from the bindings.
>>>> and some virt have it... This should be probably separate binding or if
>>>> the list is small - allOf:if:then.
>>> I attempted this; however I'm still seeing failures in dtb_check. I've added this
>>> to the binding; does this look correct?
>>>   allOf:
>>>     - $ref: qcom,rpmh-common.yaml#
>>> +  - if:
>>> +      properties:
>>> +        compatible:
>>> +          contains:
>>> +            enum:
>>> +              - qcom,qdu1000-clk-virt
>>> +              - qcom,qdu1000-mc-virt
>>> +
>>> +    then:
>>> +      required:
>>> +        - compatible
>>
>> No, because we talk about reg, not compatible. You should not require
>> reg instead for some compatibles... but then the schema is getting
>> complicated.
>>
>> It's difficult to give you recommendation because I do not know what are
>> all these "virt" interconnects. Why some have unit address, why some do not?
> 
> My understanding is that the "reg" property is required for the NoCs that have
> registers for controlling the QoS settings for the ports from Linux side.
> Other NoCs might be controlled by some remote processor and direct access from
> Linux may not be possible, so they do not have unit address and are outside of
> the soc DT node.
> Do we need to strictly define when exactly the "reg" property is required,
> can't we just mark it as optional?

It's preferred to make it strictly required or not allowed, so the
bindings are specific. This also allows to validate for mistakes. It
would be a bit different case if such test for req would make the
bindings complicated. I think it's not the case because we could just
split the bindings into two files:
1. One for controlled by AP, with reg.
2. One for controller by remote processors, without reg.

Best regards,
Krzysztof