linux-kernel - Re: [PATCH] dt-bindings: Add a RISC-V SBI firmware node

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Date:   Mon, 20 Nov 2017 21:28:56 +0100
From:   Jonathan Neuschäfer <j.neuschaefer@....net>
To:     Palmer Dabbelt <palmer@...ive.com>
Cc:     mark.rutland@....com, robh+dt@...nel.org,
        devicetree@...r.kernel.org, patches@...ups.riscv.org,
        linux-kernel@...r.kernel.org,
        Jonathan=20Neusch=C3=A4fer?= <j.neuschaefer@....net>
Subject: Re: [PATCH] dt-bindings: Add a RISC-V SBI firmware node

On Mon, Nov 20, 2017 at 11:50:00AM -0800, Palmer Dabbelt wrote:
> The RISC-V privileged ISA mandates the presence of an SBI, but there's
> no reason not to put it in the device tree.  This would allow us to
> possibly remove the SBI later.

Thanks!

> 
> CC: Jonathan Neuschäfer <j.neuschaefer@....net>
> Signed-off-by: Palmer Dabbelt <palmer@...ive.com>
> ---
>  .../devicetree/bindings/firmware/riscv.sbi.txt       | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/firmware/riscv.sbi.txt
> 
> diff --git a/Documentation/devicetree/bindings/firmware/riscv.sbi.txt b/Documentation/devicetree/bindings/firmware/riscv.sbi.txt
> new file mode 100644
> index 000000000000..42384d5d52cf
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/firmware/riscv.sbi.txt

Nit: Other bindings use either a comma (as in the compatible string,
"riscv,sbi.txt") or a dash (vendor-product.txt, "riscv-sbi.txt") in the
file name.

> @@ -0,0 +1,20 @@
> +RISC-V Supervisor Binary Interface (SBI)
> +
> +The RISC-V privileged ISA specification mandates the presence of a supervisor
> +binary interface that performs some operations which might otherwise require
> +particularly complicated instructions.  This interface includes
> +inter-processor interrupts, TLB flushes, i-cache and TLB shootdowns, a
> +console, and power management.
> +
> +Required properties:
> +- compatible: must contain one of the following
> + * "riscv,sbi" for the SBI defined by the privileged specification of the
> +   system.

"of the system" seems to imply that different RISC-V systems (different
RISC-V implementations) can have different privileged specifications.

I think it's better to refer to concrete documents, that don't depend on
the rest of the system, instead. Either:

 * "riscv,sbi" for the SBI defined by the RISC-V Privileged ISA Specification.

Or something like:

 * "sifive,sbi" for the SBI defined by SiFive document XYZ.


[ I know that there currently is no SBI spec, because the chapter has
  been removed from the Priv Spec, but this can be fixed later, once
  the final name of the document describing the SBI is clear. ]

> +
> +Example:
> +
> +firmware {
> +	sbi {
> +		compatible = "riscv,sbi";
> +	};
> +};
> -- 


Thanks,
Jonathan Neuschäfer

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