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

[Breno Leitao <leitao@debian.org>]

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 treated as a
hard failure. This causes cpuidle setup to fail entirely for all CPUs on
platforms where the FFH LPI probe returns an error.

On NVIDIA Grace (aarch64) systems with PSCIv1.1, the probe fails for all
72 CPUs with -ENODEV because psci_acpi_cpu_init_idle() finds
power.count - 1 <= 0 (power.count=1). This results in no cpuidle states
registered for any CPU, forcing them to busy-poll when idle instead of
entering low-power states.

The -ENODEV error simply means no deep PSCI idle states are available
beyond WFI, which is a normal condition. Do not propagate -ENODEV and
downgrade its message to pr_debug, while still propagating other errors
that may indicate real problems.

Fixes: cac173bea57d ("ACPI: processor: idle: Rework the handling of acpi_processor_ffh_lpi_probe()")
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/acpi/processor_idle.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index ee5facccbe10c..7b6f7730ec63d 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -1258,8 +1258,13 @@ static int acpi_processor_get_power_info(struct acpi_processor *pr)
 
 	if (pr->flags.has_lpi) {
 		ret = acpi_processor_ffh_lpi_probe(pr->id);
-		if (ret)
+		if (ret == -ENODEV) {
+			pr_debug("CPU%u: FFH LPI probe failed, err = %d, power.count = %d\n",
+				 pr->id, ret, pr->power.count);
+			ret = 0;
+		} else if (ret) {
 			pr_err("CPU%u: Invalid FFH LPI data\n", pr->id);
+		}
 	}
 
 	return ret;

---
base-commit: 66672af7a095d89f082c5327f3b15bc2f93d558e
change-id: 20260413-ffh-93f68b2f46a3

Best regards,
--  
Breno Leitao <leitao@debian.org>