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Date:   Wed, 21 Sep 2022 11:27:14 +0100
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Subject: Re: Similar SoCs with different CPUs and interrupt bindings
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To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
Cc:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Andre Przywara <andre.przywara@arm.com>,
        Conor Dooley <conor.dooley@microchip.com>,
        Samuel Holland <samuel@sholland.org>,
        Biju Das <biju.das.jz@bp.renesas.com>,
        Chris Paterson <Chris.Paterson2@renesas.com>,
        Atish Patra <atishp@atishpatra.org>,
        "Lad, Prabhakar" <prabhakar.mahadev-lad.rj@bp.renesas.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Olof Johansson <olof@lixom.net>
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From:   Robin Murphy <robin.murphy@arm.com>
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On 2022-09-21 11:17, Krzysztof Kozlowski wrote:
> On 21/09/2022 12:14, Robin Murphy wrote:
>>> +#define SOC_PERIPHERAL_IRQ_NUMBER(na)  (na + 32)
>>> +#define SOC_PERIPHERAL_IRQ(nr, na) GIC_SPI nr SOC_PERIPHERAL_IRQ_NUMBER(na)
>>>    / {
>>>           compatible = "renesas,r9a07g043";
>>>           #address-cells = <2>;
>>> @@ -128,7 +130,7 @@ ssi1: ssi@1004a000 {
>>>                           compatible = "renesas,r9a07g043-ssi",
>>>                                        "renesas,rz-ssi";
>>>                           reg = <0 0x1004a000 0 0x400>;
>>> -                       interrupts = <GIC_SPI 330 IRQ_TYPE_LEVEL_HIGH>,
>>> +                       interrupts = <SOC_PERIPHERAL_IRQ(330, IRQ_TYPE_LEVEL_HIGH)>,
>>>
>>>
>>>
>>> Or any other method like that....
>>
>> Which will generate the text:
>>
>> 	"interrupts = <GIC_SPI 330 (IRQ_TYPE_LEVEL_HIGH + 32)>,"
>>
>> (give or take some whitespace)
>>
>> CPP supports constant expressions in #if and #elif directives, but
>> macros are purely literal text replacement. It might technically be
>> achievable with some insane CPP metaprogramming, but for all practical
>> purposes this is a non-starter unless dtc itself grows the ability to
>> process arithmetic expressions.
> 
> Except I put it into flags, not to IRQ number, it works, so I am not
> sure why do you call it non-starter?

Oh, it seems dtc *does* understand arithmetic already, that's what I was 
missing.

$ echo "/dts-v1/;/{foo = <(2 + 3)>;};" | dtc -Odts
/dts-v1/;

/ {
         foo = <0x05>;
};

Thanks for teaching me something new!

Robin.