[PATCH RFC v4 08/15] ACPI: Warn when the present bit changes but the feature is not enabled

[Russell King (Oracle)]

From: James Morse <james.morse at arm.com>

ACPI firmware can trigger the events to add and remove CPUs, but the
OS may not support this.

Print an error message when this happens.

This gives early warning on arm64 systems that don't support
CONFIG_ACPI_HOTPLUG_PRESENT_CPU, as making CPUs not present has
side effects for other parts of the system.

Signed-off-by: James Morse <james.morse at arm.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron at huawei.com>
Reviewed-by: Gavin Shan <gshan at redhat.com>
Tested-by: Miguel Luis <miguel.luis at oracle.com>
Tested-by: Vishnu Pajjuri <vishnu at os.amperecomputing.com>
Tested-by: Jianyong Wu <jianyong.wu at arm.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel at armlinux.org.uk>
---
Changes since RFC v2:
 * Update commit message with suggestion from Gavin Shan
---
 drivers/acpi/acpi_processor.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index 77d47e6c2474..d1d33e74216c 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -189,8 +189,10 @@ static int acpi_processor_make_present(struct acpi_processor *pr)
 	acpi_status status;
 	int ret;
 
-	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_CPU))
+	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_CPU)) {
+		pr_err_once("Changing CPU present bit is not supported\n");
 		return -ENODEV;
+	}
 
 	if (invalid_phys_cpuid(pr->phys_id))
 		return -ENODEV;
@@ -462,8 +464,10 @@ static void acpi_processor_make_not_present(struct acpi_device *device)
 {
 	struct acpi_processor *pr;
 
-	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_CPU))
+	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_CPU)) {
+		pr_err_once("Changing CPU present bit is not supported");
 		return;
+	}
 
 	pr = acpi_driver_data(device);
 	if (pr->id >= nr_cpu_ids)
-- 
2.30.2