linux-kernel - Re: [RFC PATCH v3 05/11] dt-bindings: interrupt-controller: Add ACLINT MSWI and SSWI bindings

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Date:   Wed, 1 Sep 2021 19:33:48 -0500
From:   Rob Herring <robh@...nel.org>
To:     Anup Patel <anup@...infault.org>
Cc:     Anup Patel <anup.patel@....com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Atish Patra <atish.patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>, Bin Meng <bmeng.cn@...il.com>
Subject: Re: [RFC PATCH v3 05/11] dt-bindings: interrupt-controller: Add
 ACLINT MSWI and SSWI bindings

On Wed, Sep 1, 2021 at 6:56 AM Anup Patel <anup@...infault.org> wrote:
>
> On Wed, Sep 1, 2021 at 6:54 AM Rob Herring <robh@...nel.org> wrote:
> >
> > On Mon, Aug 30, 2021 at 09:47:23AM +0530, Anup Patel wrote:
> > > We add DT bindings documentation for the ACLINT MSWI and SSWI
> > > devices found on RISC-V SOCs.
> > >
> > > Signed-off-by: Anup Patel <anup.patel@....com>
> > > Reviewed-by: Bin Meng <bmeng.cn@...il.com>
> > > ---
> > >  .../riscv,aclint-swi.yaml                     | 95 +++++++++++++++++++
> > >  1 file changed, 95 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/interrupt-controller/riscv,aclint-swi.yaml
> > >
> > > diff --git a/Documentation/devicetree/bindings/interrupt-controller/riscv,aclint-swi.yaml b/Documentation/devicetree/bindings/interrupt-controller/riscv,aclint-swi.yaml
> > > new file mode 100644
> > > index 000000000000..68563259ae24
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/interrupt-controller/riscv,aclint-swi.yaml
> > > @@ -0,0 +1,95 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/interrupt-controller/riscv,aclint-swi.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: RISC-V ACLINT Software Interrupt Devices
> > > +
> > > +maintainers:
> > > +  - Anup Patel <anup.patel@....com>
> > > +
> > > +description:
> > > +  RISC-V SOCs include an implementation of the M-level software interrupt
> > > +  (MSWI) device and the S-level software interrupt (SSWI) device defined
> > > +  in the RISC-V Advanced Core Local Interruptor (ACLINT) specification.
> > > +
> > > +  The ACLINT MSWI and SSWI devices are documented in the RISC-V ACLINT
> > > +  specification located at
> > > +  https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc.
> > > +
> > > +  The ACLINT MSWI and SSWI devices directly connect to the M-level and
> > > +  S-level software interrupt lines of various HARTs (or CPUs) respectively
> > > +  so the RISC-V per-HART (or per-CPU) local interrupt controller is the
> > > +  parent interrupt controller for the ACLINT MSWI and SSWI devices.
> > > +
> > > +allOf:
> > > +  - $ref: /schemas/interrupt-controller.yaml#
> > > +
> > > +properties:
> > > +  compatible:
> > > +    oneOf:
> > > +      - items:
> > > +        - enum:
> > > +          - riscv,aclint-mswi
> > > +
> > > +      - items:
> > > +        - enum:
> > > +          - riscv,aclint-sswi
> >
> > All this can be just:
> >
> > enum:
> >   - riscv,aclint-mswi
> >   - riscv,aclint-sswi
> >
> > However...
> >
> > > +
> > > +    description:
> > > +      For ACLINT MSWI devices, it should be "riscv,aclint-mswi" OR
> > > +      "<vendor>,<chip>-aclint-mswi".
> > > +      For ACLINT SSWI devices, it should be "riscv,aclint-sswi" OR
> > > +      "<vendor>,<chip>-aclint-sswi".
> >
> > s/OR/AND/
> >
> > There must be a compatible for the implementation. Unless RiscV
> > implementations of specs are complete describing all clocks, power
> > domains, resets, etc. and are quirk free.
> >
> > But don't write free form constraints...
>
> It is possible that quite a few implementations (QEMU, FPGAs, and
> other simulators) will not require implementation specific compatible
> strings. Should we still mandate implementation specific compatible
> strings in DTS for such cases?

No, but the schema says you only have those cases. Are there not any
actual implementations?

Minimally make "<vendor>,<chip>-aclint-mswi" into a schema pattern for
the first entry and perhaps a note to replace with actual strings when
there are some. It's ultimately up to the RiscV maintainers to require
SoC specific compatibles here. Allowing a generic one alone makes that
harder because the schema can't enforce it.

Rob