[PATCH] ACPI: processor: Add cpuidle driver check in acpi_processor_register_idle_driver

[Tony W Wang-oc]

Commit 7a8c994cbb2d ("ACPI: processor: idle: Optimize ACPI idle
driver registration") moved the ACPI idle driver registration to
acpi_processor_driver_init(), but it didn't check whether a cpuidle
driver was already registered.

For example, on Intel platforms, if the intel_idle driver is already
loaded, the code would still evaluate the _CST object in the ACPI
table and attempt to register the acpi_idle driver. This registration
would fail with -EBUSY due to the existing check in cpuidle_register_driver.

Add a check at the beginning of acpi_processor_register_idle_driver()
to avoid unnecessary _CST evaluate and potential registration failures.

Fixes: 7a8c994cbb2d ("ACPI: processor: idle: Optimize ACPI idle driver registration") 
Signed-off-by: Tony W Wang-oc <TonyWWang-oc@xxxxxxxxxxx>
---
 drivers/acpi/processor_idle.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index ee5facccbe10..0409411abb83 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -1355,6 +1355,11 @@ void acpi_processor_register_idle_driver(void)
 	int ret = -ENODEV;
 	int cpu;
 
+	if (cpuidle_get_driver()) {
+		pr_debug("cpuidle driver %pS already registered.\n", cpuidle_get_driver());
+		return;
+	}
+
 	acpi_processor_update_max_cstate();
 
 	/*
-- 
2.25.1