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

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Message-ID: <932aaefd-e2ca-ef26-bf30-e315fb271ec5@sholland.org>
Date:   Sat, 20 Aug 2022 12:24:55 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     Conor.Dooley@...rochip.com, andre.przywara@....com
Cc:     wens@...e.org, jernej.skrabec@...il.com,
        linux-sunxi@...ts.linux.dev, palmer@...belt.com,
        paul.walmsley@...ive.com, aou@...s.berkeley.edu,
        linux-riscv@...ts.infradead.org, robh+dt@...nel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        krzysztof.kozlowski+dt@...aro.org
Subject: Re: [PATCH 06/12] riscv: dts: allwinner: Add the D1 SoC base
 devicetree

On 8/15/22 12:01 PM, Conor.Dooley@...rochip.com wrote:
> On 15/08/2022 14:11, Andre Przywara wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>
>> On Mon, 15 Aug 2022 00:08:09 -0500
>> Samuel Holland <samuel@...lland.org> wrote:
>>
>> Hi,
>>
>> thanks for all the efforts in getting those SoC peripherals supported!
>>
>>> D1 is a SoC containing a single-core T-HEAD Xuantie C906 CPU, as well as
>>> one HiFi 4 DSP. The SoC is based on a design that additionally contained
>>> a pair of Cortex A7's. For that reason, some peripherals are duplicated.
>>
>> So because of this, the Allwinner R528 and T113 SoCs would share almost
>> everything in this file. Would it be useful to already split this DT up?
>> To have a base .dtsi, basically this file without /cpus and /soc/plic,
>> then have a RISC-V specific file with just those, including the base?
>> There is precedence for this across-arch(-directories) sharing with the
>> Raspberry Pi and Allwinner H3/H5 SoCs.
> 
> For those playing along at home, one example is the arm64 bananapi m2
> dts which looks like:
>> /dts-v1/;
>> #include "sun50i-h5.dtsi"
>> #include "sun50i-h5-cpu-opp.dtsi"
>> #include <arm/sunxi-bananapi-m2-plus-v1.2.dtsi>
>>
>> / {
>> 	model = "Banana Pi BPI-M2-Plus v1.2 H5";
>> 	compatible = "bananapi,bpi-m2-plus-v1.2", "allwinner,sun50i-h5";
>> };
> 
> I think this is a pretty good idea, and putting in the modularity up
> front seems logical to me, so when the arm one does eventually get
> added it can be done by only touching a single arch.

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.

Regards,
Samuel