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

[Anup Patel]

On Tue, Nov 22, 2022 at 10:46 AM Palmer Dabbelt <palmer at rivosinc.com> wrote:
>
> On Mon, 21 Nov 2022 19:45:07 PST (-0800), anup at brainfault.org wrote:
> > On Tue, Nov 22, 2022 at 2:27 AM Palmer Dabbelt <palmer at rivosinc.com> wrote:
> >>
> >> From: Palmer Dabbelt <palmer at rivosinc.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 at rivosinc.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.

Adding a separate timer DT node, creates a new set of compatibility
issues for existing platforms. I am fine updating my series to have
separate timer DT node but do we want to go in this direction ?

Even if ARM has a separate timer DT node, the timers are still part
of the CPU. It depends on how we see the DT bindings aligning with
actual HW.

>
> > 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.

This is not a new problem we are facing. Even in the ARM world,
the DT bindings grew organically over time based on newer platform
requirements.

Now that we have a platform which does not want the time
C3STOP feature, we need to first come-up with DT bindings
to support this platform instead of temporarily disabling
features which don't work on this platform.

Regards,
Anup

>
> > 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
> >>