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

Sudeep Holla
2022-07-27T12:46:20Z

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@ventanamicro.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.

> 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