PCI: conditional resource-reallocation through kernel parameter pci=realloc

Multiple attempts to dynamically reallocate pci resources have
unfortunately lead to regressions. Though we continue to fix the
regressions and fine tune the dynamic-reallocation behavior, we have not
reached a acceptable state yet.
    
This patch provides a interim solution. It disables dynamic reallocation
by default, but adds the ability to enable it through pci=realloc kernel
command line parameter.
    
Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

Documentation/kernel-parameters.txt

@@ -2015,6 +2015,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 				the default.
 				off: Turn ECRC off
 				on: Turn ECRC on.
+		realloc		reallocate PCI resources if allocations done by BIOS
+				are erroneous.
 
 	pcie_aspm=	[PCIE] Forcibly enable or disable PCIe Active State Power
 			Management.

drivers/pci/pci.c

@@ -3483,6 +3483,8 @@ static int __init pci_setup(char *str)
 				pci_no_msi();
 			} else if (!strcmp(str, "noaer")) {
 				pci_no_aer();
+			} else if (!strncmp(str, "realloc", 7)) {
+				pci_realloc();
 			} else if (!strcmp(str, "nodomains")) {
 				pci_no_domains();
 			} else if (!strncmp(str, "cbiosize=", 9)) {

drivers/pci/pci.h

@@ -146,6 +146,8 @@ static inline void pci_no_msi(void) { }
 static inline void pci_msi_init_pci_dev(struct pci_dev *dev) { }
 #endif
 
+extern void pci_realloc(void);
+
 static inline int pci_no_d1d2(struct pci_dev *dev)
 {
 	unsigned int parent_dstates = 0;

drivers/pci/setup-bus.c

@@ -47,6 +47,13 @@ struct resource_list_x {
 	(head)->next = NULL;				\
 } while (0)
 
+int pci_realloc_enable = 0;
+#define pci_realloc_enabled() pci_realloc_enable
+void pci_realloc(void)
+{
+	pci_realloc_enable = 1;
+}
+
 /**
  * add_to_list() - add a new resource tracker to the list
  * @head:	Head of the list
@@ -1025,6 +1032,7 @@ static int __init pci_get_max_depth(void)
 	return depth;
 }
 
+
 /*
  * first try will not touch pci bridge res
  * second  and later try will clear small leaf bridge res
@@ -1068,6 +1076,13 @@ again:
 	/* any device complain? */
 	if (!head.next)
 		goto enable_and_dump;
+
+	/* don't realloc if asked to do so */
+	if (!pci_realloc_enabled()) {
+		free_list(resource_list_x, &head);
+		goto enable_and_dump;
+	}
+
 	failed_type = 0;
 	for (list = head.next; list;) {
 		failed_type |= list->flags;