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

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Date:   Thu, 8 Sep 2022 22:42:06 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     Conor Dooley <conor.dooley@...rochip.com>, andre.przywara@....com
Cc:     Jessica Clarke <jrtc27@...c27.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        devicetree <devicetree@...r.kernel.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Linux Kernel Mailing List <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

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:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>
>>
>>>> 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.

My other concern is that the big interrupt-map property would make DT overlays
even more painful to deal with. I don't think overlays can append to a property,
only replace it.

Regards,
Samuel