[PATCH RFC] ACPI: processor: idle: Do not propagate acpi_processor_ffh_lpi_probe() -ENODEV

[Rafael J. Wysocki]

On Wed, Apr 15, 2026 at 3:32 AM lihuisong (C) <lihuisong at huawei.com> wrote:
>
>
> On 4/14/2026 8:25 PM, Sudeep Holla wrote:
> > On Tue, Apr 14, 2026 at 07:31:29PM +0800, lihuisong (C) wrote:
> >> On 4/14/2026 6:21 PM, Breno Leitao wrote:
> >>> Hello Huisong,
> >>>
> >>> On Tue, Apr 14, 2026 at 05:43:51PM +0800, lihuisong (C) wrote:
> >>>> But it is a real issue. Thanks for your report.
> >>>> I think the best way to fix your issue is that remove this verification in
> >>>> psci_acpi_cpu_init_idle().
> >>>> Because it is legal for platform to report one LPI state.
> >>>> This function just needs to verify the LPI states which are FFH.
> >>> Thank you for the prompt feedback.
> >>>
> >>> Would this approach work?
> >>>
> >>> commit 6c9d52840a4f778cc989838ba76ee51416e85de3
> >>> Author: Breno Leitao <leitao at debian.org>
> >>> Date:   Tue Apr 14 03:16:08 2026 -0700
> >>>
> >>>       ACPI: processor: idle: Allow platforms with only one LPI state
> >>>       psci_acpi_cpu_init_idle() rejects platforms where power.count - 1 <= 0
> >>>       by returning -ENODEV. However, having a single LPI state (WFI) is a
> >>>       valid configuration. The function's purpose is to verify FFH idle states,
> >>>       and when count is zero, there are simply no FFH states to validate —
> >>>       this is not an error.
> >>>       On NVIDIA Grace (aarch64) systems with PSCIv1.1, power.count is 1 for
> >>>       all 72 CPUs, so the probe fails with -ENODEV. After commit cac173bea57d
> >>>       ("ACPI: processor: idle: Rework the handling of
> >>>       acpi_processor_ffh_lpi_probe()"), this failure propagates up and prevents
> >>>       cpuidle registration entirely.
> >>>       Change the check from (count <= 0) to (count < 0) so that platforms
> >>>       with only WFI are accepted. The for loop naturally handles count == 0
> >>>       by not iterating.
> >>>       Fixes: cac173bea57d ("ACPI: processor: idle: Rework the handling of acpi_processor_ffh_lpi_probe()")
> >>>       Signed-off-by: Breno Leitao <leitao at debian.org>
> >>>
> >>> diff --git a/drivers/acpi/arm64/cpuidle.c b/drivers/acpi/arm64/cpuidle.c
> >>> index 801f9c4501425..7791b751042ce 100644
> >>> --- a/drivers/acpi/arm64/cpuidle.c
> >>> +++ b/drivers/acpi/arm64/cpuidle.c
> >>> @@ -31,7 +31,7 @@ static int psci_acpi_cpu_init_idle(unsigned int cpu)
> >>>             return -EOPNOTSUPP;
> >>>     count = pr->power.count - 1;
> >>> -   if (count <= 0)
> >>> +   if (count < 0)
> >>>             return -ENODEV;
> >>>     for (i = 0; i < count; i++) {
> >> This count already verified in acpi_processor_get_lpi_info.
> >>
> >> I suggest modifing it as below:
> >>
> >> -->
> >>
> >> git diff
> >> diff --git a/drivers/acpi/arm64/cpuidle.c b/drivers/acpi/arm64/cpuidle.c
> >> index 801f9c450142..c68a5db8ebba 100644
> >> --- a/drivers/acpi/arm64/cpuidle.c
> >> +++ b/drivers/acpi/arm64/cpuidle.c
> >> @@ -16,7 +16,7 @@
> >>
> >>   static int psci_acpi_cpu_init_idle(unsigned int cpu)
> >>   {
> >> -       int i, count;
> >> +       int i;
> >>          struct acpi_lpi_state *lpi;
> >>          struct acpi_processor *pr = per_cpu(processors, cpu);
> >>
> >> @@ -30,14 +30,10 @@ static int psci_acpi_cpu_init_idle(unsigned int cpu)
> >>          if (!psci_ops.cpu_suspend)
> >>                  return -EOPNOTSUPP;
> >>
> >> -       count = pr->power.count - 1;
> >> -       if (count <= 0)
> >> -               return -ENODEV;
> >> -
> > It was intentionally designed this way, as there is little value in defining
> > only WFI in the _LPI tables. In the absence of a cpuidle driver/LPI entry,
> > arch_cpu_idle() is invoked, which is sufficient and avoids unnecessary
> > complexity, only to ultimately execute wfi() anyway.
> Yeah, it's correct. The code flow will be more simple and high-efficiency.
> This looks good to me.
>
>
> But cpuidle sysfs under per CPU is created when firmware just reports
> WFI state before
> my commit cac173bea57d ("ACPI: processor: idle: Rework the handling of
> acpi_processor_ffh_lpi_probe()").
> However, these platforms will no longer be created now and some
> statistics for state0 are also missing.
> This change in behavor is visiable to user space.I'm not sure if it is
> acceptable.
> What do you think, Rafael?

I think that it would be good to restore the previous behavior,
especially if it has been changed inadvertently.