linux-kernel - Re: Similar SoCs with different CPUs and interrupt bindings

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Date:   Wed, 21 Sep 2022 10:49:40 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     Andre Przywara <andre.przywara@....com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Samuel Holland <samuel@...lland.org>,
        Biju Das <biju.das.jz@...renesas.com>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Atish Patra <atishp@...shpatra.org>,
        "Lad, Prabhakar" <prabhakar.mahadev-lad.rj@...renesas.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>
Subject: Re: Similar SoCs with different CPUs and interrupt bindings

On 21/09/2022 09:46, Geert Uytterhoeven wrote:
>         Hi Rob, Krzysztof,
> 
> This is a topic that came up at the RISC-V BoF at Plumbers, and it was
> suggested to bring it up with you.

I guess you also need SoC maintainers as well (+Cc Arnd and Olof). :)

> 
> The same SoC may be available with either RISC-V or other (e.g. ARM) CPU
> cores (an example of this are the Renesas RZ/Five and RZ/G2UL SoCs).
> To avoid duplication, we would like to have:
>   - <riscv-soc>.dtsi includes <base-soc>.dtsi,
>   - <arm-soc>.dtsi includes <base-soc>.dtsi.
> 
> Unfortunately RISC-V and ARM typically use different types of interrupt
> controllers, using different bindings (e.g. 2-cell vs. 3-cell), and
> possibly using different interrupt numbers.  Hence the interrupt-parent
> and interrupts{-extended} properties should be different, too.
> 
> Possible solutions[1]:
>   1. interrupt-map
> 
>   2. Use a SOC_PERIPHERAL_IRQ() macro in interrupts properties in
>      <base-soc>.dtsi, with
>        - #define SOC_PERIPHERAL_IRQ(nr, na) nr          // RISC-V
>        - #define SOC_PERIPHERAL_IRQ(nr, na) GIC_SPI na  // ARM
>      Note that the cpp/dtc combo does not support arithmetic, so even
>      the simple case where nr = 32 + na cannot be simplified.

What do you mean? Macros support string concatenation and simple
arithmetic like adding numbers. I just tested it.

> 
>   3. Wrap inside RISCV() and ARM() macros, e.g.:
> 
>         RISCV(interrupts = <412 IRQ_TYPE_LEVEL_HIGH>;)
>         ARM(interrupts = <GIC_SPI 380 IRQ_TYPE_LEVEL_HIGH>;)
> 
>      Cfr. ARM() and THUMB() in arch/arm/include/asm/unified.h, as used
>      to express the same operation using plain ARM or ARM Thumb
>      instructions.
> 
> Personally, I'm leaning towards the third solution, as it is the most
> flexible, and allows us to extend to more than 2 interrupt controllers.
> 
> Note that this is actually not a new issue.  For years, ARM SoCs have
> existed with multiple types of cores on the same die, using Cortex-A
> cores for the application, and Cortex-R/SuperH/V850/... cores for
> real-time and/or baseband operation.  So far this wasn't an issue, as
> only the Cortex-A cores ran Linux, and we ignored the other cores (and
> the related interrupt controllers and hierarchy) in DT.
> 
> What do you think?
> Thanks for your comments!


If it is doable with a macro (option 2), I would vote for this. Assuming
of course that the interrupts differ only by GIC_SPI/PPI and base
number. I guess this should be the case if this is the same SoC?

Best regards,
Krzysztof