[PATCH v3] PCI: of_property: Omit bus properties without a subordinate bus

[Bjorn Helgaas <helgaas@kernel.org>]

Author: Angel J <iamanaws@httpd.dev>

PCI: of_property: Omit bus properties without a subordinate bus

A bridge (a device with a Type 1 header) may not have a secondary bus
allocated (pdev->subordinate), e.g., if there are no available bus numbers
or the bridge secondary/subordinate bus numbers are not writable.

The dynamic OF helpers of_pci_prop_bus_range() and of_pci_prop_intr_map()
dereference pdev->subordinate without checking it.  When
CONFIG_PCI_DYNAMIC_OF_NODES is enabled, this can cause a NULL pointer
dereference and early boot hang.

Generate 'bus-range' and 'interrupt-map' properties only when a subordinate
bus exists.  Keep the node and its remaining properties for bridges without
one.

The problem was latent since 407d1a51921e ("PCI: Create device tree node
for bridge"), but wasn't reachable until 1f340724419e ("PCI: of: Create
device tree PCI host bridge node"), which appeared in v6.15.  Before
1f340724419e, of_pci_make_dev_node() returned early because the parent OF
node was missing.

Fixes: 407d1a51921e ("PCI: Create device tree node for bridge")
Signed-off-by: Angel J <iamanaws@httpd.dev>
[bhelgaas: move pdev->subordinate test to callees, commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org	# v6.6+
Link: https://patch.msgid.link/20260912043106.10715-1-iamanaws@httpd.dev
---
Changes in v3:
- Move pdev->subordinate tests to of_pci_prop_bus_range() and
  of_pci_prop_intr_map()

Changes in v2
(https://lore.kernel.org/all/20260912043106.10715-1-iamanaws@httpd.dev):
- Keep the dynamic OF node and skip only bus-range and interrupt-map
  when no subordinate bus exists, following review of v1.
- Tested on Linux 6.18.44 with the v1 guard removed.

v1
(https://lore.kernel.org/all/20260911230420.26244-1-iamanaws@httpd.dev)

diff --git a/drivers/pci/of_property.c b/drivers/pci/of_property.c
index 75a358f73e69..1500740cc55d 100644
--- a/drivers/pci/of_property.c
+++ b/drivers/pci/of_property.c
@@ -95,9 +95,13 @@ static int of_pci_prop_bus_range(struct pci_dev *pdev,
 				 struct of_changeset *ocs,
 				 struct device_node *np)
 {
-	u32 bus_range[] = { pdev->subordinate->busn_res.start,
-			    pdev->subordinate->busn_res.end };
+	u32 bus_range[2];
 
+	if (!pdev->subordinate)
+		return 0;
+
+	bus_range[0] = pdev->subordinate->busn_res.start;
+	bus_range[1] = pdev->subordinate->busn_res.end;
 	return of_changeset_add_prop_u32_array(ocs, np, "bus-range", bus_range,
 					       ARRAY_SIZE(bus_range));
 }
@@ -220,6 +224,9 @@ static int of_pci_prop_intr_map(struct pci_dev *pdev, struct of_changeset *ocs,
 	int ret;
 	u8 pin;
 
+	if (!pdev->subordinate)
+		return 0;
+
 	pnode = pci_device_to_OF_node(pdev->bus->self);
 	if (!pnode)
 		pnode = pci_bus_to_OF_node(pdev->bus);