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

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Message-ID: <538ae41e-664f-2efb-f941-9a063b727b6a@microchip.com>
Date:   Mon, 22 Aug 2022 12:13:42 +0000
From:   <Conor.Dooley@...rochip.com>
To:     <geert@...ux-m68k.org>, <andre.przywara@....com>
CC:     <devicetree@...r.kernel.org>, <aou@...s.berkeley.edu>,
        <samuel@...lland.org>, <linux-kernel@...r.kernel.org>,
        <jernej.skrabec@...il.com>,
        <prabhakar.mahadev-lad.rj@...renesas.com>, <wens@...e.org>,
        <robh+dt@...nel.org>, <palmer@...belt.com>,
        <krzysztof.kozlowski+dt@...aro.org>, <paul.walmsley@...ive.com>,
        <linux-riscv@...ts.infradead.org>, <linux-sunxi@...ts.linux.dev>
Subject: Re: [PATCH 06/12] riscv: dts: allwinner: Add the D1 SoC base
 devicetree

Hey Geert,

On 22/08/2022 12:46, Geert Uytterhoeven wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Hi Conor, Andre,
> 
> 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?

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?

> 
> 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.

Thanks,
Conor.