linux-kernel - Re: [PATCH v4 2/3] dt-bindings: timer: Add bindings for the RISC-V timer device

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Message-ID: <174d93be-bedf-bf8c-4a66-284931a997b3@sholland.org>
Date:   Tue, 29 Nov 2022 22:45:22 -0600
From:   Samuel Holland <samuel@...lland.org>
To:     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>
Cc:     Andrew Jones <ajones@...tanamicro.com>,
        Atish Patra <atishp@...shpatra.org>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Anup Patel <anup@...infault.org>, devicetree@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/3] dt-bindings: timer: Add bindings for the RISC-V
 timer device

On 11/29/22 08:03, 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>
> Reviewed-by: Conor Dooley <conor.dooley@...rochip.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:

I don't want to derail getting this merged, but if you do end up sending
another version, could you please spell out the word "cannot" here and
in the code? The missing apostrophe makes this jarring (and an entirely
different word).

> +    type: boolean
> +    description:
> +      If present, the timer interrupt can't wake up the CPU from
> +      suspend/idle state.

And in that case I would also suggest clarifying this as "one or more
suspend/idle states", since the limitation does not apply to all idle
states. At least it should never apply to the architectural WFI state;
for the SBI idle state binding, it only applies to those with the
"local-timer-stop" property.

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

The CLINT and PLIC bindings also include the M-mode interrupts. Should
we do the same here?

Regards,
Samuel