[+cc Lijo]
On Tue, Oct 27, 2026 at 11:22:25AM -0500, Mario Limonciello wrote:
> 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 <[email protected]>
> ---
> 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;
I think I was mistaken to suggest that pci_bus was the right place to
store this.
It seems like we definitely need something in the pci_dev because we
may clear the initial bus numbers in the first pass, so we need to
stash the secondary bus number somewhere until the second pass
allocates the pci_bus and we can save it here.
Since we have to have it in the pci_dev, I suspect maybe it would be
enough to have it *only* there. Maybe it could be set in
pci_read_bridge_windows(), and drivers could find it via
pdev->bus->self?
> 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;
I think you're right to use "secondary" here so we don't perpetuate
the "subordinate" misuse. Maybe also include "initial" and make it
"unsigned char" so it's the same as pci_bus.number?
> 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
>
