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

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Date:   Wed, 27 Jul 2022 17:59:59 +0530
From:   Anup Patel <apatel@...tanamicro.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     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>,
        Anup Patel <anup@...infault.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

On Wed, Jul 27, 2022 at 5:48 PM Sudeep Holla <sudeep.holla@....com> wrote:
>
> On Wed, Jul 27, 2022 at 05:13:01PM +0530, 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.
> >
>
> I don't have much idea on idle states on RISC-V but associating this
> property in just CPU node seems like not so good idea.
>
> This will be applicable for all CPU idle states which means you
> can't use this even if one of the deepest idle state switches off
> the timer.
>
> We have local-timer-stop in each idle states node. IIRC RISC-V uses the
> binding which is now not arm specific[0] and IIRC you moved the binding
> yourself. Any reason why not can't be used and any specific reason for
> needing this extra property.

Indeed, the "local-timer-stop" property should be used. I guess,
Allwinner D1 should use this property in idle state and we should
not unconditionally set CLOCK_EVT_FEAT_C3STOP in the timer
driver.

@Samuel Holland Can you confirm that the "local-timer-stop" property
works for Allwinner D1 ? If yes, then please send a patch to remove
CLOCK_EVT_FEAT_C3STOP from timer driver.

Regards,
Anup