Re: [PATCH v4 06/10] dt-bindings: riscv: Add bouffalolab bl808 board compatibles

[Jisheng Zhang]

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@xxxxxxxxxx>
> > > Acked-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
> > > Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> > > ---
> > >  .../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@xxxxxxxxxx>
> > > +
> > > +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 {
	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.