linux-kernel - Re: [PATCH 06/12] riscv: dts: allwinner: Add the D1 SoC base devicetree

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Date:   Wed, 21 Sep 2022 09:49:59 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Samuel Holland <samuel@...lland.org>
Cc:     Conor Dooley <conor.dooley@...rochip.com>,
        Andre Przywara <andre.przywara@....com>,
        Jessica Clarke <jrtc27@...c27.com>,
        devicetree <devicetree@...r.kernel.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        "Lad, Prabhakar" <prabhakar.mahadev-lad.rj@...renesas.com>,
        Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH 06/12] riscv: dts: allwinner: Add the D1 SoC base devicetree

On Fri, Sep 9, 2022 at 9:10 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Fri, Sep 9, 2022 at 5:42 AM Samuel Holland <samuel@...lland.org> wrote:
> > On 8/22/22 10:29 AM, Jessica Clarke wrote:
> > > On 22 Aug 2022, at 14:56, conor.dooley@...rochip.com wrote:
> > >> On 22/08/2022 13:31, Geert Uytterhoeven wrote:
> > >>>> Do you think this is worth doing? Or are you just providing an
> > >>>> example of what could be done?
> > >>>
> > >>> Just some brainstorming...
> > >>>
> > >>>> Where would you envisage putting these macros? I forget the order
> > >>>> of the CPP operations that are done, can they be put in the dts?
> > >>>
> > >>> The SOC_PERIPHERAL_IRQ() macro should be defined in the
> > >>> ARM-based SoC.dtsi file and the RISC-V-based SoC.dtsi file.
> > >>
> > >> Right, one level up but ~the same result.
> > >>
> > >>>>> Nice! But it's gonna be a very large interrupt-map.
> > >>>>
> > >>>> I quite like the idea of not duplicating files across the archs
> > >>>> if it can be helped, but not at the expense of making them hard to
> > >>>> understand & I feel like unfortunately the large interrupt map is
> > >>>> in that territory.
> > >>>
> > >>> I feel the same.
> > >>> Even listing both interrupt numbers in SOC_PERIPHERAL_IRQ(na, nr)
> > >>> is a risk for making mistakes.
> > >>>
> > >>> So personally, I'm in favor of teaching dtc arithmetic, so we can
> > >>> handle the offset in SOC_PERIPHERAL_IRQ().
> > >>
> > >> Yup, in the same boat here. mayb I'll get bored enough to bite..
> > >
> > > Note that GPL’ed dtc isn’t the only implementation. FreeBSD uses a
> > > BSD-licensed implementation[1] and so adding new features like this to
> > > GPL dtc that actually get used would require us to reimplement it too.
> > > I don’t know how much effort it would be but please keep this in mind.
> >
> > I plan to go with the "SOC_PERIPHERAL_IRQ(na, nr)" implementation for v2. I like
> > that it only affects the DT source, and does not leak into the DTB. We still
> > have the freedom to switch to using arithmetic later when all of the tools
> > support it.
>
> May I suggest an alternative solution, which would be more generic,
> and can be extended to other/more CPU cores easily:
>
> Specify both interrupts in the .dtsi, but wrapped inside e.g. ARM()
> resp. RISCV() macros:
>
>     ARM(interrupts = <GIC_SPI 380 IRQ_TYPE_LEVEL_HIGH>;)
>     RISCV(interrupts = <412 IRQ_TYPE_LEVEL_HIGH>;)
>
> The same construct can be used for e.g. interrupt-parent.
> The ARM .dts would define:
>
>     #define ARM(x...)    x
>     #define RISCV(x....)
>
> before including the .dtsi.
> The RISC-V DTS would define instead:
>
>     #define ARM(x...)
>     #define RISCV(x...)    x
>
> Cfr. the AR_CLASS(), M_CLASS(), ARM(), and THUMB() macros in
> arch/arm/include/asm/unified.h.

I brought it up with the DT people in a separate thread[1].
Please continue the discussion there.
Thanks!

[1] https://lore.kernel.org/r/CAMuHMdUPm36RsxHdVwspR3NCAR3C507AyB6R65W42N2gXWq0ag@mail.gmail.com

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds