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Message-ID: <CAAhSdy1zSdqk5B-DBv5puEutT9+5s86QRw4UpjbgkLsiXGurCQ@mail.gmail.com>
Date: Thu, 1 Dec 2022 11:26:47 +0530
From: Anup Patel <anup@...infault.org>
To: Samuel Holland <samuel@...lland.org>
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>,
Conor Dooley <conor.dooley@...rochip.com>,
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 Wed, Nov 30, 2022 at 10:15 AM Samuel Holland <samuel@...lland.org> wrote:
>
> 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).
Okay, I will update.
>
> > + 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.
Okay, I will update.
>
> > +
> > +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?
The RISC-V timer uses SBI time extension or RISC-V Sstc extension hence
it is only for S-mode software. In other words, the RISC-V timer is a S-mode
only timer.
The M-mode software is supposed to have its own platform specific MMIO
based timer.
Regards,
Anup
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