[PATCH v4 1/3] PCI: Preserve the initial bus number in pci_bus

[Mario Limonciello]

Bridge scans are split into two passes when bus numbers need reassigning.
Save the firmware secondary bus number on the bridge in pass 0, before it
is disabled. Use it to initialize number_initial when the child bus is
created in pass 1, before bus registration callbacks run.

Keep the saved secondary number on the bridge so a later rescan does not
replace the child's initial number with its reassigned runtime number.

Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
 drivers/pci/probe.c | 6 ++++++
 include/linux/pci.h | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 27008e2ea5afc..3c03ac22223d9 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1012,6 +1012,7 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	bus->sysdata = bridge->sysdata;
 	bus->ops = bridge->ops;
 	bus->number = bus->busn_res.start = bridge->busnr;
+	bus->number_initial = bus->number;
 #ifdef CONFIG_PCI_DOMAINS_GENERIC
 	if (bridge->domain_nr == PCI_DOMAIN_NR_NOT_SET)
 		bus->domain_nr = pci_bus_find_domain_nr(bus, parent);
@@ -1232,6 +1233,8 @@ static struct pci_bus *pci_alloc_child_bus(struct pci_bus *parent,
 
 	/* Set up the primary, secondary and subordinate bus numbers */
 	child->number = child->busn_res.start = busnr;
+	child->number_initial = bridge && bridge->bridge_secondary_busnr ?
+		bridge->bridge_secondary_busnr : busnr;
 	child->primary = parent->busn_res.start;
 	child->busn_res.end = 0xff;
 
@@ -1418,6 +1421,8 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
 
 	pci_dbg(dev, "scanning [bus %02x-%02x] behind bridge, pass %d\n",
 		secondary, subordinate, pass);
+	if (!pass && !dev->bridge_secondary_busnr)
+		dev->bridge_secondary_busnr = secondary;
 
 	if (!primary && (primary != bus->number) && secondary && subordinate) {
 		pci_warn(dev, "Primary bus is hard wired to 0\n");
@@ -1470,6 +1475,7 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
 			child = pci_add_new_bus(bus, dev, secondary);
 			if (!child)
 				goto out;
+			child->number_initial = secondary;
 			child->primary = primary;
 			pci_bus_insert_busn_res(child, secondary, subordinate);
 			child->bridge_ctl = bctl;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 5ffcf5ce8c966..c607818a98a87 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -363,6 +363,8 @@ struct pci_dev {
 	struct pci_slot	*slot;		/* Physical slot this device is in */
 
 	unsigned int	devfn;		/* Encoded device & function index */
+	/* Firmware secondary bus number saved across bridge scan passes */
+	u8		bridge_secondary_busnr;
 	unsigned short	vendor;
 	unsigned short	device;
 	unsigned short	subsystem_vendor;
@@ -724,6 +726,7 @@ struct pci_bus {
 	struct proc_dir_entry *procdir;	/* Directory entry in /proc/bus/pci */
 
 	unsigned char	number;		/* Bus number */
+	unsigned char	number_initial;	/* Bus number before reassignment */
 	unsigned char	primary;	/* Number of primary bridge */
 	unsigned char	max_bus_speed;	/* enum pci_bus_speed */
 	unsigned char	cur_bus_speed;	/* enum pci_bus_speed */

-- 
2.43.0