linux-kernel - Re: [PATCH] cpuidle: riscv-sbi: Stop using non-retentive suspend

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Message-ID: <CAAhSdy0Fs9ZVoRgtz92RgLnFPvgwUzCP_KpK9SCOiVsA-t3p3Q@mail.gmail.com>
Date:   Tue, 22 Nov 2022 09:15:07 +0530
From:   Anup Patel <anup@...infault.org>
To:     Palmer Dabbelt <palmer@...osinc.com>
Cc:     Conor Dooley <conor@...nel.org>, rafael@...nel.org,
        daniel.lezcano@...aro.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>, aou@...s.berkeley.edu,
        linux-pm@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux@...osinc.com
Subject: Re: [PATCH] cpuidle: riscv-sbi: Stop using non-retentive suspend

On Tue, Nov 22, 2022 at 2:27 AM Palmer Dabbelt <palmer@...osinc.com> wrote:
>
> From: Palmer Dabbelt <palmer@...osinc.com>
>
> As per [1], whether or not the core can wake up from non-retentive
> suspend is a platform-specific detail.  We don't have any way to encode
> that, so just stop using them until we've sorted that out.
>
> Link: https://github.com/riscv-non-isa/riscv-sbi-doc/issues/98#issuecomment-1288564687
> Fixes: 6abf32f1d9c5 ("cpuidle: Add RISC-V SBI CPU idle driver")
> Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>

This is just unnecessary maintenance churn and it's not the
right way to go. Better to fix this the right way instead of having
a temporary fix.

I had already sent-out a patch series 5 months back to describe
this in DT:
https://lore.kernel.org/lkml/20220727114302.302201-1-apatel@ventanamicro.com/

No one has commented/suggested anything (except Samuel
Holland and Sudeep Holla).

Please review this series. I can quickly address comments to
make this available for Linux-6.2. Until this series is merged,
the affected platforms can simply remove non-retentive suspend
states from their DT.

With all due respect, NACK to this patch from my side.

Regards,
Anup

>
> ---
>
> This should allow us to revert 232ccac1bd9b ("clocksource/drivers/riscv:
> Events are stopped during CPU suspend"), which fixes suspend on the D1
> but breaks timers everywhere.
> ---
>  drivers/cpuidle/cpuidle-riscv-sbi.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/drivers/cpuidle/cpuidle-riscv-sbi.c b/drivers/cpuidle/cpuidle-riscv-sbi.c
> index 05fe2902df9a..9d1063a54495 100644
> --- a/drivers/cpuidle/cpuidle-riscv-sbi.c
> +++ b/drivers/cpuidle/cpuidle-riscv-sbi.c
> @@ -214,6 +214,17 @@ static bool sbi_suspend_state_is_valid(u32 state)
>         if (state > SBI_HSM_SUSPEND_NON_RET_DEFAULT &&
>             state < SBI_HSM_SUSPEND_NON_RET_PLATFORM)
>                 return false;
> +
> +       /*
> +        * Whether or not RISC-V systems deliver interrupts to harts in a
> +        * non-retentive suspend state is a platform-specific detail.  This can
> +        * leave the hart unable to wake up, so just mark these states as
> +        * unsupported until we have a mechanism to expose these
> +        * platform-specific details to Linux.
> +        */
> +       if (state & SBI_HSM_SUSP_NON_RET_BIT)
> +               return false;
> +
>         return true;
>  }
>
> --
> 2.38.1
>