linux-kernel - Re: [PATCH 6/6] riscv: dts: microchip: add the mpfs' fabric clock control

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Message-ID: <f8496006-7487-7b7e-1a53-ec38492dfe70@microchip.com>
Date:   Fri, 19 Aug 2022 14:14:36 +0000
From:   <Conor.Dooley@...rochip.com>
To:     <krzysztof.kozlowski@...aro.org>, <mturquette@...libre.com>,
        <sboyd@...nel.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <palmer@...belt.com>,
        <Daire.McNamara@...rochip.com>
CC:     <paul.walmsley@...ive.com>, <aou@...s.berkeley.edu>,
        <linux-clk@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH 6/6] riscv: dts: microchip: add the mpfs' fabric clock
 control

On 19/08/2022 15:06, Krzysztof Kozlowski wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On 19/08/2022 16:48, Conor.Dooley@...rochip.com wrote:
>> On 19/08/2022 14:28, Krzysztof Kozlowski wrote:
>>>> Maybe that is me exploiting the "should", but I was not sure how to
>>>> include the location in the devicetree.
>>>
>>> Neither node names nor clock names are considered an ABI, but some
>>> pieces like to rely on them. Now you created such dependency so imagine
>>> someone prepares a DTSI/DTS with "clock-controller" names for all four
>>> blocks. How you driver would behave?
>>
>> -EEXIST, registration fails in the core.
>>
>>> The DTS would be perfectly valid but driver would not accept it
>>> (conflicting names) or behave incorrect.
>>>
>>> I think what you need is the clock-output-names property. The core
>>> schema dtschema/schemas/clock/clock.yaml recommends unified
>>> interpretation of it - list of names for all the clocks - but accepts
>>> other uses, e.g. as a prefix.
>>
>> So could I do `clock-output-names = "ccc_nw";`. That would work for me,
>> with one question:
>> How would I enforce the unique-ness of this property, since it would be
>> a per CCC/clock-controller property? Maybe I missed something, but I
>> gave it a shot with two different CCC nodes having "ccc_nw" & dtbs_check
>> did not complain. Up to me to explain the restriction in the dt-bindings
>> description?
> 
> Uniqueness among entire DTS? I don't think you can, except of course
> mentioning it in description. Your driver should handle such DTS -
> minimally by gracefully failing but better behaving in some default way.

It fails not-too-gracefully at the moment, but that could easily be
changed. Truncated base address I suppose would be a meaningful thing
to fall back to afterwards.

> 
>>
>> FWIW I would then have:
>> ccc_sw: clock-controller@...00000 {
>>        compatible = "microchip,mpfs-ccc";
>>        reg = <0x0 0x38400000 0x0 0x1000>, <0x0 0x38800000 0x0 0x1000>,
>>              <0x0 0x39400000 0x0 0x1000>, <0x0 0x39800000 0x0 0x1000>;
>>        #clock-cells = <1>;
>>        clock-output-names = "ccc_sw";
>>        status = "disabled";
>> };
>>
>> & in the binding:
>>     clock-output-names:
>>       pattern: ^ccc_[ns][ew]$
> 
> Yes, although this won't enforce uniqueness.

I know :( I'll respin next week I guess, thanks again.
Conor.