PCI: Delay enabling bridges until they're needed

We currently enable PCI bridges after scanning a bus and assigning
resources.  This is often done in arch code.

This patch changes this so we don't enable a bridge until necessary, i.e.,
until we enable a PCI device behind the bridge.  We do this in the generic
pci_enable_device() path, so this also removes the arch-specific code to
enable bridges.

[bhelgaas: changelog]
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

arch/arm/kernel/bios32.c

@@ -525,11 +525,6 @@ void pci_common_init_dev(struct device *parent, struct hw_pci *hw)
 			 * Assign resources.
 			 */
 			pci_bus_assign_resources(bus);
-
-			/*
-			 * Enable bridges
-			 */
-			pci_enable_bridges(bus);
 		}
 
 		/*

arch/m68k/platform/coldfire/pci.c

@@ -319,7 +319,6 @@ static int __init mcf_pci_init(void)
 	pci_fixup_irqs(pci_common_swizzle, mcf_pci_map_irq);
 	pci_bus_size_bridges(rootbus);
 	pci_bus_assign_resources(rootbus);
-	pci_enable_bridges(rootbus);
 	return 0;
 }
 

arch/mips/pci/pci.c

@@ -113,7 +113,6 @@ static void pcibios_scanbus(struct pci_controller *hose)
 		if (!pci_has_flag(PCI_PROBE_ONLY)) {
 			pci_bus_size_bridges(bus);
 			pci_bus_assign_resources(bus);
-			pci_enable_bridges(bus);
 		}
 	}
 }

arch/sh/drivers/pci/pci.c

@@ -69,7 +69,6 @@ static void pcibios_scanbus(struct pci_channel *hose)
 
 		pci_bus_size_bridges(bus);
 		pci_bus_assign_resources(bus);
-		pci_enable_bridges(bus);
 	} else {
 		pci_free_resource_list(&resources);
 	}

drivers/acpi/pci_root.c

@@ -527,9 +527,6 @@ static int acpi_pci_root_add(struct acpi_device *device,
 	if (system_state != SYSTEM_BOOTING) {
 		pcibios_resource_survey_bus(root->bus);
 		pci_assign_unassigned_bus_resources(root->bus);
-
-		/* need to after hot-added ioapic is registered */
-		pci_enable_bridges(root->bus);
 	}
 
 	pci_bus_add_devices(root->bus);

drivers/parisc/lba_pci.c

@@ -1590,7 +1590,6 @@ lba_driver_probe(struct parisc_device *dev)
 		lba_dump_res(&lba_dev->hba.lmmio_space, 2);
 #endif
 	}
-	pci_enable_bridges(lba_bus);
 
 	/*
 	** Once PCI register ops has walked the bus, access to config

drivers/pci/bus.c

@@ -216,24 +216,6 @@ void pci_bus_add_devices(const struct pci_bus *bus)
 	}
 }
 
-void pci_enable_bridges(struct pci_bus *bus)
-{
-	struct pci_dev *dev;
-	int retval;
-
-	list_for_each_entry(dev, &bus->devices, bus_list) {
-		if (dev->subordinate) {
-			if (!pci_is_enabled(dev)) {
-				retval = pci_enable_device(dev);
-				if (retval)
-					dev_err(&dev->dev, "Error enabling bridge (%d), continuing\n", retval);
-				pci_set_master(dev);
-			}
-			pci_enable_bridges(dev->subordinate);
-		}
-	}
-}
-
 /** pci_walk_bus - walk devices on/under bus, calling callback.
  *  @top      bus whose devices should be walked
  *  @cb       callback to be called for each device found
@@ -301,4 +283,3 @@ EXPORT_SYMBOL(pci_bus_put);
 EXPORT_SYMBOL(pci_bus_alloc_resource);
 EXPORT_SYMBOL_GPL(pci_bus_add_device);
 EXPORT_SYMBOL(pci_bus_add_devices);
-EXPORT_SYMBOL(pci_enable_bridges);

drivers/pci/hotplug/acpiphp_glue.c

@@ -723,7 +723,6 @@ static int __ref enable_device(struct acpiphp_slot *slot)
 	acpiphp_sanitize_bus(bus);
 	acpiphp_set_hpp_values(bus);
 	acpiphp_set_acpi_region(slot);
-	pci_enable_bridges(bus);
 
 	list_for_each_entry(dev, &bus->devices, bus_list) {
 		/* Assume that newly added devices are powered on already. */

drivers/pci/pci.c

@@ -1145,6 +1145,24 @@ int pci_reenable_device(struct pci_dev *dev)
 	return 0;
 }
 
+static void pci_enable_bridge(struct pci_dev *dev)
+{
+	int retval;
+
+	if (!dev)
+		return;
+
+	pci_enable_bridge(dev->bus->self);
+
+	if (pci_is_enabled(dev))
+		return;
+	retval = pci_enable_device(dev);
+	if (retval)
+		dev_err(&dev->dev, "Error enabling bridge (%d), continuing\n",
+			retval);
+	pci_set_master(dev);
+}
+
 static int pci_enable_device_flags(struct pci_dev *dev, unsigned long flags)
 {
 	int err;
@@ -1165,6 +1183,8 @@ static int pci_enable_device_flags(struct pci_dev *dev, unsigned long flags)
 	if (atomic_inc_return(&dev->enable_cnt) > 1)
 		return 0;		/* already enabled */
 
+	pci_enable_bridge(dev->bus->self);
+
 	/* only skip sriov related */
 	for (i = 0; i <= PCI_ROM_RESOURCE; i++)
 		if (dev->resource[i].flags & flags)

drivers/pci/probe.c

@@ -1979,7 +1979,6 @@ unsigned int __ref pci_rescan_bus(struct pci_bus *bus)
 
 	max = pci_scan_child_bus(bus);
 	pci_assign_unassigned_bus_resources(bus);
-	pci_enable_bridges(bus);
 	pci_bus_add_devices(bus);
 
 	return max;

drivers/pci/setup-bus.c

@@ -1440,7 +1440,7 @@ pci_assign_unassigned_root_bus_resources(struct pci_bus *bus)
 
 	/* any device complain? */
 	if (list_empty(&fail_head))
-		goto enable_and_dump;
+		goto dump;
 
 	if (tried_times >= pci_try_num) {
 		if (enable_local == undefined)
@@ -1449,7 +1449,7 @@ pci_assign_unassigned_root_bus_resources(struct pci_bus *bus)
 			dev_info(&bus->dev, "Automatically enabled pci realloc, if you have problem, try booting with pci=realloc=off\n");
 
 		free_list(&fail_head);
-		goto enable_and_dump;
+		goto dump;
 	}
 
 	dev_printk(KERN_DEBUG, &bus->dev,
@@ -1482,10 +1482,7 @@ pci_assign_unassigned_root_bus_resources(struct pci_bus *bus)
 
 	goto again;
 
-enable_and_dump:
-	/* Depth last, update the hardware. */
-	pci_enable_bridges(bus);
-
+dump:
 	/* dump the resource on buses */
 	pci_bus_dump_resources(bus);
 }
@@ -1556,7 +1553,6 @@ void pci_assign_unassigned_bridge_resources(struct pci_dev *bridge)
 	if (retval)
 		dev_err(&bridge->dev, "Error reenabling bridge (%d)\n", retval);
 	pci_set_master(bridge);
-	pci_enable_bridges(parent);
 }
 EXPORT_SYMBOL_GPL(pci_assign_unassigned_bridge_resources);
 

drivers/pcmcia/cardbus.c

@@ -91,7 +91,6 @@ int __ref cb_alloc(struct pcmcia_socket *s)
 	if (s->tune_bridge)
 		s->tune_bridge(s, bus);
 
-	pci_enable_bridges(bus);
 	pci_bus_add_devices(bus);
 
 	return 0;

include/linux/pci.h

@@ -1043,7 +1043,6 @@ int __must_check pci_bus_alloc_resource(struct pci_bus *bus,
 						  resource_size_t,
 						  resource_size_t),
 			void *alignf_data);
-void pci_enable_bridges(struct pci_bus *bus);
 
 /* Proper probing supporting hot-pluggable devices */
 int __must_check __pci_register_driver(struct pci_driver *, struct module *,