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

[lihuisong (C)]

On 4/15/2026 10:03 PM, Rafael J. Wysocki wrote:
> 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.
Agreed.

Can you send it again using my proposal, @breno?
We can send out other patch to discuss it if need to optimize the point 
Sudeep mentioned.
>