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Date:   Fri, 19 Aug 2022 17:06:58 +0300
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Subject: Re: [PATCH 6/6] riscv: dts: microchip: add the mpfs' fabric clock
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To:     Conor.Dooley@microchip.com, mturquette@baylibre.com,
        sboyd@kernel.org, robh+dt@kernel.org,
        krzysztof.kozlowski+dt@linaro.org, palmer@dabbelt.com,
        Daire.McNamara@microchip.com
Cc:     paul.walmsley@sifive.com, aou@eecs.berkeley.edu,
        linux-clk@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org
References: <20220819122259.183600-1-conor.dooley@microchip.com>
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From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
In-Reply-To: <19ca2ca1-c678-c669-4214-e92416e37191@microchip.com>
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On 19/08/2022 16:48, Conor.Dooley@microchip.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.

> 
> FWIW I would then have:
> ccc_sw: clock-controller@38400000 {
> 	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.

Best regards,
Krzysztof