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

[lihuisong (C)]

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;
-
-       for (i = 0; i < count; i++) {
+       for (i = 1; i < pr->power.count; i++) {
                 u32 state;

-               lpi = &pr->power.lpi_states[i + 1];
+               lpi = &pr->power.lpi_states[i];
                 /*
                  * Only bits[31:0] represent a PSCI power_state while
                  * bits[63:32] must be 0x0 as per ARM ACPI FFH 
Specification