Merge tag 'acpi-pci-4.1-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm

Pull PCI / ACPI fix from Rafael Wysocki:
 "This fixes a bug uncovered by a recent driver core change that
  modified the implementation of the ACPI_COMPANION_SET() macro to
  strictly rely on its second argument to be either NULL or a valid
  pointer to struct acpi_device.

  As it turns out, pcibios_root_bridge_prepare() on x86 and ia64 works
  with the assumption that the only code path calling pci_create_root_bus()
  is pci_acpi_scan_root() and therefore the sysdata argument passed to
  it will always match the expectations of pcibios_root_bridge_prepare().

  That need not be the case, however, and in particular it is not the
  case for the Xen pcifront driver that passes a pointer to its own
  private data strcture as sysdata to pci_scan_bus_parented() which then
  passes it to pci_create_root_bus() and it ends up being used incorrectly
  by pcibios_root_bridge_prepare()"

* tag 'acpi-pci-4.1-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
  PCI / ACPI: Do not set ACPI companions for host bridges with parents

arch/ia64/pci/pci.c

@@ -478,9 +478,16 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
 
 int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
 {
-	struct pci_controller *controller = bridge->bus->sysdata;
-
-	ACPI_COMPANION_SET(&bridge->dev, controller->companion);
+	/*
+	 * We pass NULL as parent to pci_create_root_bus(), so if it is not NULL
+	 * here, pci_create_root_bus() has been called by someone else and
+	 * sysdata is likely to be different from what we expect.  Let it go in
+	 * that case.
+	 */
+	if (!bridge->dev.parent) {
+		struct pci_controller *controller = bridge->bus->sysdata;
+		ACPI_COMPANION_SET(&bridge->dev, controller->companion);
+	}
 	return 0;
 }
 

arch/x86/pci/acpi.c

@@ -482,9 +482,16 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
 
 int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
 {
-	struct pci_sysdata *sd = bridge->bus->sysdata;
-
-	ACPI_COMPANION_SET(&bridge->dev, sd->companion);
+	/*
+	 * We pass NULL as parent to pci_create_root_bus(), so if it is not NULL
+	 * here, pci_create_root_bus() has been called by someone else and
+	 * sysdata is likely to be different from what we expect.  Let it go in
+	 * that case.
+	 */
+	if (!bridge->dev.parent) {
+		struct pci_sysdata *sd = bridge->bus->sysdata;
+		ACPI_COMPANION_SET(&bridge->dev, sd->companion);
+	}
 	return 0;
 }