PCI: Assign PCI domain IDs by ida_alloc()

Replace assignment of PCI domain IDs from atomic_inc_return() to
ida_alloc().

Use two IDAs, one for static domain allocations (those which are defined in
device tree) and second for dynamic allocations (all other).

During removal of root bus / host bridge, also release the domain ID.  The
released ID can be reused again, for example when dynamically loading and
unloading native PCI host bridge drivers.

This change also allows to mix static device tree assignment and dynamic by
kernel as all static allocations are reserved in dynamic pool.

[bhelgaas: set "err" if "bus->domain_nr < 0"]
Link: https://lore.kernel.org/r/20220714184130.5436-1-pali@kernel.org
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Author: pali

drivers/pci/pci.c

@@ -6743,67 +6743,84 @@ static void pci_no_domains(void)
 }
 
 #ifdef CONFIG_PCI_DOMAINS_GENERIC
-static atomic_t __domain_nr = ATOMIC_INIT(-1);
+static DEFINE_IDA(pci_domain_nr_static_ida);
+static DEFINE_IDA(pci_domain_nr_dynamic_ida);
 
-static int pci_get_new_domain_nr(void)
+static void of_pci_reserve_static_domain_nr(void)
 {
-	return atomic_inc_return(&__domain_nr);
+	struct device_node *np;
+	int domain_nr;
+
+	for_each_node_by_type(np, "pci") {
+		domain_nr = of_get_pci_domain_nr(np);
+		if (domain_nr < 0)
+			continue;
+		/*
+		 * Permanently allocate domain_nr in dynamic_ida
+		 * to prevent it from dynamic allocation.
+		 */
+		ida_alloc_range(&pci_domain_nr_dynamic_ida,
+				domain_nr, domain_nr, GFP_KERNEL);
+	}
 }
 
 static int of_pci_bus_find_domain_nr(struct device *parent)
 {
-	static int use_dt_domains = -1;
-	int domain = -1;
+	static bool static_domains_reserved = false;
+	int domain_nr;
 
-	if (parent)
-		domain = of_get_pci_domain_nr(parent->of_node);
+	/* On the first call scan device tree for static allocations. */
+	if (!static_domains_reserved) {
+		of_pci_reserve_static_domain_nr();
+		static_domains_reserved = true;
+	}
+
+	if (parent) {
+		/*
+		 * If domain is in DT, allocate it in static IDA.  This
+		 * prevents duplicate static allocations in case of errors
+		 * in DT.
+		 */
+		domain_nr = of_get_pci_domain_nr(parent->of_node);
+		if (domain_nr >= 0)
+			return ida_alloc_range(&pci_domain_nr_static_ida,
+					       domain_nr, domain_nr,
+					       GFP_KERNEL);
+	}
 
 	/*
-	 * Check DT domain and use_dt_domains values.
-	 *
-	 * If DT domain property is valid (domain >= 0) and
-	 * use_dt_domains != 0, the DT assignment is valid since this means
-	 * we have not previously allocated a domain number by using
-	 * pci_get_new_domain_nr(); we should also update use_dt_domains to
-	 * 1, to indicate that we have just assigned a domain number from
-	 * DT.
-	 *
-	 * If DT domain property value is not valid (ie domain < 0), and we
-	 * have not previously assigned a domain number from DT
-	 * (use_dt_domains != 1) we should assign a domain number by
-	 * using the:
-	 *
-	 * pci_get_new_domain_nr()
-	 *
-	 * API and update the use_dt_domains value to keep track of method we
-	 * are using to assign domain numbers (use_dt_domains = 0).
-	 *
-	 * All other combinations imply we have a platform that is trying
-	 * to mix domain numbers obtained from DT and pci_get_new_domain_nr(),
-	 * which is a recipe for domain mishandling and it is prevented by
-	 * invalidating the domain value (domain = -1) and printing a
-	 * corresponding error.
+	 * If domain was not specified in DT, choose a free ID from dynamic
+	 * allocations. All domain numbers from DT are permanently in
+	 * dynamic allocations to prevent assigning them to other DT nodes
+	 * without static domain.
 	 */
-	if (domain >= 0 && use_dt_domains) {
-		use_dt_domains = 1;
-	} else if (domain < 0 && use_dt_domains != 1) {
-		use_dt_domains = 0;
-		domain = pci_get_new_domain_nr();
-	} else {
-		if (parent)
-			pr_err("Node %pOF has ", parent->of_node);
-		pr_err("Inconsistent \"linux,pci-domain\" property in DT\n");
-		domain = -1;
-	}
+	return ida_alloc(&pci_domain_nr_dynamic_ida, GFP_KERNEL);
+}
 
-	return domain;
+static void of_pci_bus_release_domain_nr(struct pci_bus *bus, struct device *parent)
+{
+	if (bus->domain_nr < 0)
+		return;
+
+	/* Release domain from IDA where it was allocated. */
+	if (of_get_pci_domain_nr(parent->of_node) == bus->domain_nr)
+		ida_free(&pci_domain_nr_static_ida, bus->domain_nr);
+	else
+		ida_free(&pci_domain_nr_dynamic_ida, bus->domain_nr);
 }
 
 int pci_bus_find_domain_nr(struct pci_bus *bus, struct device *parent)
 {
 	return acpi_disabled ? of_pci_bus_find_domain_nr(parent) :
 			       acpi_pci_bus_find_domain_nr(bus);
 }
+
+void pci_bus_release_domain_nr(struct pci_bus *bus, struct device *parent)
+{
+	if (!acpi_disabled)
+		return;
+	of_pci_bus_release_domain_nr(bus, parent);
+}
 #endif
 
 /**

drivers/pci/probe.c

@@ -906,6 +906,10 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 		bus->domain_nr = pci_bus_find_domain_nr(bus, parent);
 	else
 		bus->domain_nr = bridge->domain_nr;
+	if (bus->domain_nr < 0) {
+		err = bus->domain_nr;
+		goto free;
+	}
 #endif
 
 	b = pci_find_bus(pci_domain_nr(bus), bridge->busnr);
@@ -1030,6 +1034,9 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	device_del(&bridge->dev);
 
 free:
+#ifdef CONFIG_PCI_DOMAINS_GENERIC
+	pci_bus_release_domain_nr(bus, parent);
+#endif
 	kfree(bus);
 	return err;
 }

drivers/pci/remove.c

@@ -160,6 +160,12 @@ void pci_remove_root_bus(struct pci_bus *bus)
 	pci_remove_bus(bus);
 	host_bridge->bus = NULL;
 
+#ifdef CONFIG_PCI_DOMAINS_GENERIC
+	/* Release domain_nr if it was dynamically allocated */
+	if (host_bridge->domain_nr == PCI_DOMAIN_NR_NOT_SET)
+		pci_bus_release_domain_nr(bus, host_bridge->dev.parent);
+#endif
+
 	/* remove the host bridge */
 	device_del(&host_bridge->dev);
 }

include/linux/pci.h

@@ -1726,6 +1726,7 @@ static inline int acpi_pci_bus_find_domain_nr(struct pci_bus *bus)
 { return 0; }
 #endif
 int pci_bus_find_domain_nr(struct pci_bus *bus, struct device *parent);
+void pci_bus_release_domain_nr(struct pci_bus *bus, struct device *parent);
 #endif
 
 /* Some architectures require additional setup to direct VGA traffic */