PCI: Add 'nodomains' boot option, and pci_domains_supported global

* Introduce pci_domains_supported global, hardcoded to zero if
  !CONFIG_PCI_DOMAINS.

* Introduce 'nodomains' boot option, which clears pci_domains_supported
  on platforms that enable it by default (x86, x86-64, and others when
  they are converted to use this).
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Documentation/kernel-parameters.txt

@@ -1274,6 +1274,8 @@ and is between 256 and 4096 characters. It is defined in the file
 		noaer		[PCIE] If the PCIEAER kernel config parameter is
 				enabled, this kernel boot option can be used to
 				disable the use of PCIE advanced error reporting.
+		nodomains	[PCI] Disable support for multiple PCI
+				root domains (aka PCI segments, in ACPI-speak).
 		nommconf	[X86-32,X86_64] Disable use of MMCONFIG for PCI
 				Configuration
 		nomsi		[MSI] If the PCI_MSI kernel config parameter is

drivers/pci/pci.c

@@ -23,6 +23,10 @@
 
 unsigned int pci_pm_d3_delay = 10;
 
+#ifdef CONFIG_PCI_DOMAINS
+int pci_domains_supported = 1;
+#endif
+
 #define DEFAULT_CARDBUS_IO_SIZE		(256)
 #define DEFAULT_CARDBUS_MEM_SIZE	(64*1024*1024)
 /* pci=cbmemsize=nnM,cbiosize=nn can override this */
@@ -1567,6 +1571,13 @@ int pci_select_bars(struct pci_dev *dev, unsigned long flags)
 	return bars;
 }
 
+static void __devinit pci_no_domains(void)
+{
+#ifdef CONFIG_PCI_DOMAINS
+	pci_domains_supported = 0;
+#endif
+}
+
 static int __devinit pci_init(void)
 {
 	struct pci_dev *dev = NULL;
@@ -1588,6 +1599,8 @@ static int __devinit pci_setup(char *str)
 				pci_no_msi();
 			} else if (!strcmp(str, "noaer")) {
 				pci_no_aer();
+			} else if (!strcmp(str, "nodomains")) {
+				pci_no_domains();
 			} else if (!strncmp(str, "cbiosize=", 9)) {
 				pci_cardbus_io_size = memparse(str + 9, &str);
 			} else if (!strncmp(str, "cbmemsize=", 10)) {

include/linux/pci.h

@@ -685,13 +685,16 @@ extern void pci_unblock_user_cfg_access(struct pci_dev *dev);
  * a PCI domain is defined to be a set of PCI busses which share
  * configuration space.
  */
-#ifndef CONFIG_PCI_DOMAINS
+#ifdef CONFIG_PCI_DOMAINS
+extern int pci_domains_supported;
+#else
+enum { pci_domains_supported = 0 };
 static inline int pci_domain_nr(struct pci_bus *bus) { return 0; }
 static inline int pci_proc_domain(struct pci_bus *bus)
 {
 	return 0;
 }
-#endif
+#endif /* CONFIG_PCI_DOMAINS */
 
 #else /* CONFIG_PCI is not enabled */