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

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Date:   Mon, 21 Nov 2022 21:16:40 -0800 (PST)
From:   Palmer Dabbelt <palmer@...osinc.com>
To:     anup@...infault.org
CC:     Conor Dooley <conor@...nel.org>, rafael@...nel.org,
        daniel.lezcano@...aro.org,
        Paul Walmsley <paul.walmsley@...ive.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 Mon, 21 Nov 2022 19:45:07 PST (-0800), anup@...infault.org wrote:
> 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).

I see some comments from Krzysztof here 
<https://lore.kernel.org/lkml/7a0477a0-9f0f-87d6-4070-30321745f4cc@linaro.org/> 
as well.  Looks like everyone is pointing out that having our CPU nodes 
encode timers is a bad idea, my guess is that they're probably right.

> 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.

That leaves us with a dependency between kernel versions and DT 
bindings: kernels with the current driver will result in broken systems 
with the non-retentive suspend states in the DT they boot with when 
those states can't wake up the CPU.

> 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
>>