linux-kernel - Re: [PATCH v2 1/2] dt-bindings: riscv: Add optional DT property riscv,timer-can-wake-cpu

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Message-ID: <CAAhSdy0TSKhR8_2eU7pmgizybuxPbwAycn4YudvkfGWGbnXNtQ@mail.gmail.com>
Date:   Wed, 27 Jul 2022 19:15:28 +0530
From:   Anup Patel <anup@...infault.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        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 v2 1/2] dt-bindings: riscv: Add optional DT property riscv,timer-can-wake-cpu

Hi Sudeep,

On Wed, Jul 27, 2022 at 6:16 PM Sudeep Holla <sudeep.holla@....com> wrote:
>
> On Wed, Jul 27, 2022 at 02:07:50PM +0200, Krzysztof Kozlowski wrote:
> > On 27/07/2022 13:43, Anup Patel wrote:
> > > We add an optional DT property riscv,timer-can-wake-cpu which if present
> > > in CPU DT node then CPU timer is always powered-on and never loses context.
> > >
> > > Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> > > ---
> > >  Documentation/devicetree/bindings/riscv/cpus.yaml | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > > index d632ac76532e..b60b64b4113a 100644
> > > --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
> > > +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > > @@ -78,6 +78,12 @@ properties:
> > >        - rv64imac
> > >        - rv64imafdc
> > >
> > > +  riscv,timer-can-wake-cpu:
> > > +    type: boolean
> > > +    description:
> > > +      If present, the timer interrupt can wake up the CPU from
> > > +      suspend/idle state.
> >
> > Isn't this a property of a timer, not CPU? IOW, your timer node should
> > have "wakeup-source" property.
> >
>
> I agree on the concept that this is property of the timer and not CPU.
> However we generally don't need to use wakeup-source property for timer
> as we ideally use this for waking up from system sleep state and we don't
> want to be running timer when we enter the state.

It seems ARM is using two separate timer DT properties: one for
system suspend (i.e. arm,no-tick-in-suspend) and another for CPU
system (i.e. always-on). Is this understanding correct ?

>
> > Now that's actual problem: why the RISC-V timer is bound to "riscv"
> > compatible, not to dedicated timer node? How is it related to actual CPU
> > (not SoC)?
>
> We have "always-on" property for this on arm arch timer, and I also see
> "regulator-always-on" or something similar defined. So in absence of timer
> node probably "local-timer-always-on" make sense ? Thoughts ?
>
> --
> Regards,
> Sudeep

Regards,
Anup