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

[Breno Leitao]

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++) {