Re: [PATCH] ACPI: arm64: cpuidle: Tolerate platforms with no deep PSCI idle states

[Sudeep Holla <sudeep.holla@kernel.org>]

On Mon, Apr 20, 2026 at 02:27:13AM -0700, Breno Leitao wrote:
> Commit cac173bea57d ("ACPI: processor: idle: Rework the handling of
> acpi_processor_ffh_lpi_probe()") moved the acpi_processor_ffh_lpi_probe()
> call from acpi_processor_setup_cpuidle_dev(), where its return value was
> ignored, to acpi_processor_get_power_info(), where it is now treated as
> a hard failure. As a result, platforms where psci_acpi_cpu_init_idle()
> returned -ENODEV stopped registering any cpuidle states, forcing CPUs to
> busy-poll when idle.
> 
> On NVIDIA Grace (aarch64) systems with PSCIv1.1, pr->power.count is 1
> (only WFI, no deep PSCI states beyond it), so the previous
> "count = pr->power.count - 1; if (count <= 0) return -ENODEV;" check
> returned -ENODEV for all 72 CPUs and disabled cpuidle entirely.
> 
> The lpi_states count is already validated in acpi_processor_get_lpi_info(),
> so the check here is redundant. Simplify the loop to iterate over
> lpi_states[1..power.count). When only WFI is present, the loop body
> simply does not execute and the function returns 0, which is the correct
> outcome: there is nothing to validate for FFH and no error to report.
> 
> Suggested-by: Huisong Li <lihuisong@huawei.com>
> Cc: stable@vger.kernel.org
> Fixes: cac173bea57d ("ACPI: processor: idle: Rework the handling of acpi_processor_ffh_lpi_probe()")
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
>  drivers/acpi/arm64/cpuidle.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/acpi/arm64/cpuidle.c b/drivers/acpi/arm64/cpuidle.c
> index 801f9c4501425..c68a5db8ebba8 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;
> -

Does it make sense to retain this check like
  if (pr->power.count < 1)
  	return -EINVAL;

Though I see the assignment to pr->power.count in drivers/acpi/processor_idle.c
is through unsigned int. So I am fine even without the above check.

Reviewed-by: Sudeep Holla <sudeep.holla@kernel.org>

-- 
Regards,
Sudeep