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

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Date:   Mon, 22 Aug 2022 14:31:41 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Conor Dooley <Conor.Dooley@...rochip.com>
Cc:     Andre Przywara <andre.przywara@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Albert Ou <aou@...s.berkeley.edu>,
        Samuel Holland <samuel@...lland.org>,
        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

Hi Conor,

On Mon, Aug 22, 2022 at 2:13 PM <Conor.Dooley@...rochip.com> wrote:
> On 22/08/2022 12:46, Geert Uytterhoeven wrote:
> > On Sun, Aug 21, 2022 at 12:07 PM <Conor.Dooley@...rochip.com> wrote:
> >> On 21/08/2022 07:45, Icenowy Zheng wrote:
> >>> 在 2022-08-20星期六的 17:29 +0000，Conor.Dooley@...rochip.com写道：
> >>>> On 20/08/2022 18:24, Samuel Holland wrote:
>
> >>>>> This is not feasible, due to the different #interrupt-cells. See
> >>>>> https://lore.kernel.org/linux-riscv/CAMuHMdXHSMcrVOH+vcrdRRF+i2TkMcFisGxHMBPUEa8nTMFpzw@mail.gmail.com/
> >>>>>
> >>>>> Even if we share some file across architectures, you still have to
> >>>>> update files
> >>>>> in both places to get the interrupts properties correct.
> >>>>>
> >>>>> I get the desire to deduplicate things, but we already deal with
> >>>>> updating the
> >>>>> same/similar nodes across several SoCs, so that is nothing new. I
> >>>>> think it would
> >>>>> be more confusing/complicated to have all of the interrupts
> >>>>> properties
> >>>>> overridden in a separate file.
> >>>>
> >>>> Yeah, should maybe have circled back after that conversation, would
> >>>> have been
> >>>> nice but if the DTC can't do it nicely then w/e.
> >>>
> >>> Well, maybe we can overuse the facility of C preprocessor?
> >>>
> >>> e.g.
> >>>
> >>> ```
> >>> // For ARM
> >>> #define SOC_PERIPHERAL_IRQ(n) GIC_SPI n
> >>> // For RISC-V
> >>> #define SOC_PERIPHERAL_IRQ(n) n
> >>> ```
> >>>
> >>
> >> Geert pointed out that this is not possible (at least on the Renesas
> >> stuff) because the GIC interrupt numbers are not the same as the
> >> PLIC's & the DTC is not able to handle the addition:
> >> https://lore.kernel.org/linux-riscv/CAMuHMdXHSMcrVOH+vcrdRRF+i2TkMcFisGxHMBPUEa8nTMFpzw@mail.gmail.com/
> >
> > Without the ability to do additions in DTC, we could e.g. list both
> > interrupts in the macro, like:
> >
> >      // For ARM
> >      #define SOC_PERIPHERAL_IRQ(na, nr) GIC_SPI na
> >      // For RISC-V
> >      #define SOC_PERIPHERAL_IRQ(na, nr) nr
>
> 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.

> > On Mon, Aug 22, 2022 at 12:52 PM Andre Przywara <andre.przywara@....com> wrote:
> >> There are interrupt-maps for that:
> >> sun8i-r528.dtsi:
> >>          soc {
> >>                  #interrupt-cells = <1>;
> >>                  interrupt-map = <0  18 &gic GIC_SPI  2 IRQ_TYPE_LEVEL_HIGH>,
> >>                                  <0  19 &gic GIC_SPI  3 IRQ_TYPE_LEVEL_HIGH>,
> >>                                  ....
> >>
> >> sun20i-d1.dtsi:
> >>          soc {
> >>                  #interrupt-cells = <1>;
> >>                  interrupt-map = <0  18 &plic  18 IRQ_TYPE_LEVEL_HIGH>,
> >>                                  <0  19 &plic  19 IRQ_TYPE_LEVEL_HIGH>,
> >>
> >> then, in the shared .dtsi:
> >>                  uart0: serial@...0000 {
> >>                          compatible = "snps,dw-apb-uart";
> >>                          ...
> >>                          interrupts = <18>;
> >
> > 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().

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