linux-kernel - Re: [PATCH v3 2/3] dt-bindings: timer: Add bindings for the RISC-V timer device

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Date:   Fri, 25 Nov 2022 19:18:48 +0530
From:   Anup Patel <anup@...infault.org>
To:     Conor Dooley <conor.dooley@...rochip.com>
Cc:     Anup Patel <apatel@...tanamicro.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Jones <ajones@...tanamicro.com>,
        Atish Patra <atishp@...shpatra.org>,
        Samuel Holland <samuel@...lland.org>,
        devicetree@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] dt-bindings: timer: Add bindings for the RISC-V
 timer device

On Fri, Nov 25, 2022 at 6:40 PM Conor Dooley <conor.dooley@...rochip.com> wrote:
>
> Hey Anup,
>
> For the future, could you please CC me on all patches in a series that I
> have previously reviewed?

Okay.

>
> On Fri, Nov 25, 2022 at 04:51:04PM +0530, Anup Patel wrote:
> > We add DT bindings for a separate RISC-V timer DT node which can
> > be used to describe implementation specific behaviour (such as
> > timer interrupt not triggered during non-retentive suspend).
> >
> > Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> > ---
> >  .../bindings/timer/riscv,timer.yaml           | 52 +++++++++++++++++++
> >  1 file changed, 52 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/timer/riscv,timer.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/timer/riscv,timer.yaml b/Documentation/devicetree/bindings/timer/riscv,timer.yaml
> > new file mode 100644
> > index 000000000000..cf53dfff90bc
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/timer/riscv,timer.yaml
> > @@ -0,0 +1,52 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/timer/riscv,timer.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: RISC-V timer
> > +
> > +maintainers:
> > +  - Anup Patel <anup@...infault.org>
> > +
> > +description: |+
> > +  RISC-V platforms always have a RISC-V timer device for the supervisor-mode
> > +  based on the time CSR defined by the RISC-V privileged specification. The
> > +  timer interrupts of this device are configured using the RISC-V SBI Time
> > +  extension or the RISC-V Sstc extension.
> > +
> > +  The clock frequency of RISC-V timer device is specified via the
> > +  "timebase-frequency" DT property of "/cpus" DT node which is described
> > +  in Documentation/devicetree/bindings/riscv/cpus.yaml
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - riscv,timer
> > +
> > +  interrupts-extended:
> > +    minItems: 1
> > +    maxItems: 4096   # Should be enough?
> > +
> > +  riscv,timer-cant-wake-cpu:
> > +    type: boolean
> > +    description:
> > +      If present, the timer interrupt can't wake up the CPU from
> > +      suspend/idle state.
>
> I'm really not sure about this... I would be inclined to think that if
> someone does not specify then we should assume that they took the
> scroogiest view of the spec and so do not get events during suspend.
>
> I suppose you could then argue that their DT is wrong & it's their fault
> though. Plus the existing platforms behave this way & we avoid having to
> retrofit stuff here.

Yes, the DT property is defined to keep things working for
existing platforms.

IMO, people should always read the DT bindings document at time of
creating DT for their platform. If there are queries then they can always
shoot email to the maintainers on LKML.

>
> > +
> > +additionalProperties: false
> > +
> > +required:
> > +  - compatible
> > +  - interrupts-extended
> > +
> > +examples:
> > +  - |
> > +    timer {
> > +      compatible = "riscv,timer";
> > +      interrupts-extended = <&cpu1intc 5>,
> > +                            <&cpu2intc 5>,
> > +                            <&cpu3intc 5>,
> > +                            <&cpu4intc 5>;
> > +    };
> > +...
> > --
> > 2.34.1
> >

Regards,
Anup