PCI: Add generic domain handling

The handling of PCI domains (or PCI segments in ACPI speak) is usually a
straightforward affair but its implementation is currently left to the
architectural code, with pci_domain_nr(b) querying the value of the domain
associated with bus b.

This patch introduces CONFIG_PCI_DOMAINS_GENERIC as an option that can be
selected if an architecture wants a simple implementation where the value
of the domain associated with a bus is stored in struct pci_bus.

The architectures that select CONFIG_PCI_DOMAINS_GENERIC will then have to
implement pci_bus_assign_domain_nr() as a way of setting the domain number
associated with a root bus.  All child buses except the root bus will
inherit the domain_nr value from their parent.

Signed-off-by: Catalin Marinas <Catalin.Marinas@arm.com>
[Renamed pci_set_domain_nr() to pci_bus_assign_domain_nr()]
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Arnd Bergmann <arnd@arndb.de>

drivers/pci/probe.c

@@ -485,7 +485,7 @@ void pci_read_bridge_bases(struct pci_bus *child)
 	}
 }
 
-static struct pci_bus *pci_alloc_bus(void)
+static struct pci_bus *pci_alloc_bus(struct pci_bus *parent)
 {
 	struct pci_bus *b;
 
@@ -500,6 +500,10 @@ static struct pci_bus *pci_alloc_bus(void)
 	INIT_LIST_HEAD(&b->resources);
 	b->max_bus_speed = PCI_SPEED_UNKNOWN;
 	b->cur_bus_speed = PCI_SPEED_UNKNOWN;
+#ifdef CONFIG_PCI_DOMAINS_GENERIC
+	if (parent)
+		b->domain_nr = parent->domain_nr;
+#endif
 	return b;
 }
 
@@ -671,7 +675,7 @@ static struct pci_bus *pci_alloc_child_bus(struct pci_bus *parent,
 	/*
 	 * Allocate a new bus, and inherit stuff from the parent..
 	 */
-	child = pci_alloc_bus();
+	child = pci_alloc_bus(parent);
 	if (!child)
 		return NULL;
 
@@ -1761,13 +1765,14 @@ struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
 	char bus_addr[64];
 	char *fmt;
 
-	b = pci_alloc_bus();
+	b = pci_alloc_bus(NULL);
 	if (!b)
 		return NULL;
 
 	b->sysdata = sysdata;
 	b->ops = ops;
 	b->number = b->busn_res.start = bus;
+	pci_bus_assign_domain_nr(b, parent);
 	b2 = pci_find_bus(pci_domain_nr(b), bus);
 	if (b2) {
 		/* If we already got to this bus through a different bridge, ignore it */