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Date:   Sun, 21 May 2023 17:45:11 +0800
From:   Jisheng Zhang <jszhang@kernel.org>
To:     Conor Dooley <conor.dooley@microchip.com>
Cc:     Samuel Holland <samuel@sholland.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
        devicetree@vger.kernel.org, linux-serial@vger.kernel.org,
        Palmer Dabbelt <palmer@rivosinc.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Marc Zyngier <maz@kernel.org>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v4 06/10] dt-bindings: riscv: Add bouffalolab bl808 board
 compatibles
Message-ID: <ZGnoJ6OrC1XvjglJ@xhacker>
References: <20230518152244.2178-1-jszhang@kernel.org>
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 <c6e44e14-35b2-da09-5e8c-4d47e7a7a055@sholland.org>
 <20230519-squad-undermine-6124aafebafa@wendy>
 <ZGnkhSlk8NaPELxh@xhacker>
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On Sun, May 21, 2023 at 05:29:47PM +0800, Jisheng Zhang wrote:
> On Fri, May 19, 2023 at 12:55:02PM +0100, Conor Dooley wrote:
> > On Thu, May 18, 2023 at 10:31:35PM -0500, Samuel Holland wrote:
> > > Hi Jisheng, DT maintainers,
> > 
> > Sick, thanks for piping up Samuel!
> > Both Rob and Krzysztof are not around at the moment, so that probably
> > leaves it up to me.. I'm adding Arnd in case he has a take here too.
> > 
> > > On 5/18/23 10:22, Jisheng Zhang wrote:
> > > > Several SoMs and boards are available that feature the Bouffalolab
> > > > bl808 SoC. Document the compatible strings.
> > > > 
> > > > Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> > > > Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
> > > > Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> > > > ---
> > > >  .../bindings/riscv/bouffalolab.yaml           | 29 +++++++++++++++++++
> > > >  1 file changed, 29 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/riscv/bouffalolab.yaml
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/riscv/bouffalolab.yaml b/Documentation/devicetree/bindings/riscv/bouffalolab.yaml
> > > > new file mode 100644
> > > > index 000000000000..3b25d1a5d04a
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/riscv/bouffalolab.yaml
> > > > @@ -0,0 +1,29 @@
> > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/riscv/bouffalolab.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: Bouffalo Lab Technology SoC-based boards
> > > > +
> > > > +maintainers:
> > > > +  - Jisheng Zhang <jszhang@kernel.org>
> > > > +
> > > > +description:
> > > > +  Bouffalo Lab Technology SoC-based boards
> > > > +
> > > > +properties:
> > > > +  $nodename:
> > > > +    const: '/'
> > > > +  compatible:
> > > > +    oneOf:
> > > > +      - description: Carrier boards for the Sipeed M1s SoM
> > > > +        items:
> > > > +          - enum:
> > > > +              - sipeed,m1s-dock
> > > > +          - const: sipeed,m1s
> > > > +          - const: bouffalolab,bl808
> > > 
> > > As mentioned in the message for patch 5, "The Bouffalolab bl808 SoC
> > > contains three riscv CPUs, namely M0, D0 and LP. The D0 is 64bit RISC-V
> > > GC compatible, so can run linux."
> > > 
> > > I have also been running U-Boot and NOMMU Linux on the less powerful,
> > > but still quite fast, "M0" core. However, this core needs a different
> 
> Just FYI, I successfully ran nommu rv32 linux kernel on the "M0" core
> with some patches to the riscv head and irqchip driver.
> 
> > > DTB because:
> > >  1) The CPU is different (T-HEAD E907 instead of C906).
> > >  2) The interrupt routing is completely different.
> > >     a. The M0 core contains a CLIC instead of a PLIC.
> > >     b. The peripherals in the SoC are split between two buses. Those
> > >        on one bus have their IRQs directly connected to M0, and share
> > >        a multiplexed IRQ connection to D0; and vice versa for the
> > >        other bus. So each bus's interrupt-parent needs to be swapped.
> > > 
> > > Using some preprocessor magic like we did for Allwinner and Renesas, I
> > > was able to share most of the SoC and board DTs between the cores[1].
> > > However, this still ends up with two DTs for each board. So here are my
> > > questions:
> > >  - Is this acceptable?
> > 
> > I expected it to look worse than it actually turned out to be.
> > I don't think Krzysztof in particular is a fan of having conditional
> > bits in dts files, but for the shared arm/riscv stuff there was not
> > really another sensible option.
> > 
> > >  - Is there precedent for how we should name the two board DTs?
> > 
> > Arnd might have some idea about precedent here, but I like your naming
> > well enough.
> > 
> > >  - How does this affect the board and SoC compatible strings?
> > >    - Should there be a separate "bouffalolab,bl808-d0" in addition to
> > >      "bouffalolab,bl808"?
> > 
> > What ordering were you intending here?
> > "pine64,0x64" "bouffalolab,bl808" "bouffalolab,bl808-d0"?
> > 
> > That doesn't really seem correct though, as it does not get less specific
> > as you move right.
> > 
> > "pine64,0x64" "bouffalolab,bl808-d0" "bouffalolab,bl808" doesn't seem
> > right either though, for the same sort of reason.
> > 
> > >    - Is it acceptable to use the same board compatible string for both,
> > >      since the _board_ part of the DT does not change, only things
> > >      inside the SoC?
> 
> what about describing the DT as the SoC is, e.g
> lp: cpu@0 {
> 	...
> 	status = disabled;
> };
> 
> m0: cpu@1 {
> 	...
> 	status = disabled;
> };
> 
> d0: cpu@2 {
> 	...
> 	status = disabled;
> };
> 
> Then in m0 dts:
> &m0 {
> 	status = okay;
> };
> 
> in d0 dts:
> &m0 {

typo: 

&d0 {

> 	status = okay;
> };
> 
> 
> > 
> > I think you may need to have 2 compatibles per board, depending on which
> > cpu. Perhaps even as verbose as:
> > "pine61,0x64-d0" "pine64,0x64" "bouffalolab,bl808-d0" "bouffalolab,bl808"
> > 
> > Not exactly straightforward though, is it!
> > 
> > > It would be possible to avoid having two DTs per board by guarding all
> > > of the differences behind "#ifdef CONFIG_64BIT", but that seems wrong
> > > because you would end up with two totally incompatible DTBs named the
> > > same thing, depending on how the DTB was built.
> > 
> > I think having 2 dtbs is fine, and as I mentioned, I've seen Krzysztof
> > complain previously about conditional bits like that.
> > 
> > Cheers,
> > Conor.
> 
>