LoongArch: Preserve firmware configuration when desired

If we must preserve the firmware resource assignments, claim the existing
resources rather than reassigning everything.

According to PCI Firmware Specification: if ACPI DSM#5 function returns
0, the OS must retain the resource allocation for PCI in the firmware; if
ACPI DSM#5 function returns 1, the OS can ignore the resource allocation
for PCI and reallocate it.

Signed-off-by: Qihang Gao <gaoqihang@loongson.cn>
Signed-off-by: Juxin Gao <gaojuxin@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

Author: chenhuacai

arch/loongarch/pci/acpi.c

@@ -194,6 +194,7 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
 {
 	struct pci_bus *bus;
 	struct pci_root_info *info;
+	struct pci_host_bridge *host;
 	struct acpi_pci_root_ops *root_ops;
 	int domain = root->segment;
 	int busnum = root->secondary.start;
@@ -237,8 +238,17 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
 			return NULL;
 		}
 
-		pci_bus_size_bridges(bus);
-		pci_bus_assign_resources(bus);
+		/* If we must preserve the resource configuration, claim now */
+		host = pci_find_host_bridge(bus);
+		if (host->preserve_config)
+			pci_bus_claim_resources(bus);
+
+		/*
+		 * Assign whatever was left unassigned. If we didn't claim above,
+		 * this will reassign everything.
+		 */
+		pci_assign_unassigned_root_bus_resources(bus);
+
 		list_for_each_entry(child, &bus->children, node)
 			pcie_bus_configure_settings(child);
 	}