ACPI / PM: Avoid infinite recurrence while registering power resources

There is at least one BIOS with a DSDT containing a power resource
object with a _PR0 entry pointing back to that power resource.  In
consequence, while registering that power resource
acpi_bus_get_power_flags() sees that it depends on itself and tries
to register it again, which leads to an infinitely deep recurrence.
This problem was introduced by commit bf325f9538
(ACPI / PM: Register power resource devices as soon as they are
needed).

To fix this problem use the observation that power resources cannot
be power manageable and prevent acpi_bus_get_power_flags() from
being called for power resource objects.

References: https://bugzilla.kernel.org/show_bug.cgi?id=31872
Reported-and-tested-by: Pascal Dormeau <pdormeau@free.fr>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Len Brown <lenb@kernel.org>
Cc: stable@kernel.org

drivers/acpi/scan.c

@@ -943,6 +943,10 @@ static int acpi_bus_get_flags(struct acpi_device *device)
 	if (ACPI_SUCCESS(status))
 		device->flags.lockable = 1;
 
+	/* Power resources cannot be power manageable. */
+	if (device->device_type == ACPI_BUS_TYPE_POWER)
+		return 0;
+
 	/* Presence of _PS0|_PR0 indicates 'power manageable' */
 	status = acpi_get_handle(device->handle, "_PS0", &temp);
 	if (ACPI_FAILURE(status))