Re: [PATCH] Revert "ACPI: processor: idle: Only flush cache on entering C3"

[Rafael J. Wysocki]

On Sun, Apr 3, 2022 at 8:25 AM Akihiko Odaki <akihiko.odaki@xxxxxxxxx> wrote:
>
> This reverts commit 87ebbb8c612b1214f227ebb8f25442c6d163e802.
>
> ACPI processor power states can be transitioned in two distinct
> situations: 1. when CPU goes idle and 2. before CPU goes offline
> ("playing dead") to suspend or hibernate. Case 1 is handled by
> acpi_idle_enter or acpi_idle_enter_s2idle. Case 2 is handled by
> acpi_idle_play_dead.
>
> It is necessary to flush CPU caches in case 2 even if it is not
> required to transit ACPI processor power states as CPU will go
> offline soon. However, the reverted commit incorrectly removed CPU
> cache flushing in such a condition.

I think what you mean is that the CPU cache must always be flushed in
acpi_idle_play_dead(), regardless of the target C-state that is going
to be requested, because this is likely to be part of a CPU offline
procedure or preparation for entering a system-wide sleep state and
the stale cache contents may lead to problems going forward, for
example when the CPU is taken back online.

If so, I will put the above information into the patch changelog.

> In fact, it made resuming from
> suspend-to-RAM occasionally fail on Lenovo ThinkPad C13 Yoga.

So this probably means that resume from suspend-to-RAM occasionally
fails on Lenovo ThinkPad C13 Yoga and reverting the commit in question
fixes this problem.  Is that correct?

> Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxx>
> ---
>  drivers/acpi/processor_idle.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index f8e9fa82cb9b..05b3985a1984 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -570,8 +570,7 @@ static int acpi_idle_play_dead(struct cpuidle_device *dev, int index)
>  {
>         struct acpi_processor_cx *cx = per_cpu(acpi_cstate[index], dev->cpu);
>
> -       if (cx->type == ACPI_STATE_C3)
> -               ACPI_FLUSH_CPU_CACHE();
> +       ACPI_FLUSH_CPU_CACHE();
>
>         while (1) {
>
> --
> 2.35.1
>