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

[Breno Leitao]

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;
> -
> -       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

Ack, I will respin.

Thanks for your help,
--breno