ACPI / PCI: pci_link: Allow the absence of _PRS and change log level

In recent Intel hardware the IRQs become non-configurable after BIOS
initializes them in PEI phase and _PRS objects are no longer included in
ASL.

This is the same as "static (non-configurable) devices do not
specify a _PRS object" in ACPI spec. As a result, error messages
saying "ACPI Exception: AE_NOT_FOUND, Evaluating _PRS" does not need to
be in kernel messenges all the time but only when debug is enabled, and
acpi_pci_link_get_possible should not return -ENODEV when _PRS is
absent.

Signed-off-by: Alex Hung <alex.hung@canonical.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/pci_link.c

@@ -173,8 +173,8 @@ static int acpi_pci_link_get_possible(struct acpi_pci_link *link)
 	status = acpi_walk_resources(link->device->handle, METHOD_NAME__PRS,
 				     acpi_pci_link_check_possible, link);
 	if (ACPI_FAILURE(status)) {
-		ACPI_EXCEPTION((AE_INFO, status, "Evaluating _PRS"));
-		return -ENODEV;
+		acpi_handle_debug(link->device->handle, "_PRS not present or invalid");
+		return 0;
 	}
 
 	ACPI_DEBUG_PRINT((ACPI_DB_INFO,