[PATCH v4] pci-bridge: avoid linking a single downstream port more than once

[Yao Xingtao]

Since the downstream port is not checked, two slots can be linked to
a single port. However, this can prevent the driver from detecting the
device properly.

It is necessary to ensure that a downstream port is not linked more than
once.

Links: 
OSZPR01MB6453BC61D2FF4035F18084EF8DDC2@OSZPR01MB6453.jpnprd01.prod.outlook.com">https://lore.kernel.org/qemu-devel/OSZPR01MB6453BC61D2FF4035F18084EF8DDC2@OSZPR01MB6453.jpnprd01.prod.outlook.com
Signed-off-by: Yao Xingtao <yaoxt.fnst@fujitsu.com>

---
V3[3] -> V4:
 - make the error message more readable
 - fix the downstream port check error

V2[2] -> V3:
 - Move this check into pcie_cap_init()

V1[1] -> V2:
 - Move downstream port check forward

[1] 
20240704033834.3362-1-yaoxt.fnst@fujitsu.com">https://lore.kernel.org/qemu-devel/20240704033834.3362-1-yaoxt.fnst@fujitsu.com
[2] 
20240717085621.55315-1-yaoxt.fnst@fujitsu.com">https://lore.kernel.org/qemu-devel/20240717085621.55315-1-yaoxt.fnst@fujitsu.com
[3] 
20240725032731.13032-1-yaoxt.fnst@fujitsu.com">https://lore.kernel.org/qemu-devel/20240725032731.13032-1-yaoxt.fnst@fujitsu.com
---
 hw/pci/pcie.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
index 4b2f0805c6e0..1e53be1bc7c5 100644
--- a/hw/pci/pcie.c
+++ b/hw/pci/pcie.c
@@ -192,6 +192,13 @@ int pcie_cap_init(PCIDevice *dev, uint8_t offset,
 
     assert(pci_is_express(dev));
 
+    if ((type == PCI_EXP_TYPE_DOWNSTREAM || type == PCI_EXP_TYPE_ROOT_PORT) &&
+        pcie_find_port_by_pn(pci_get_bus(dev), port)) {
+        error_setg(errp, "The port %d is already in use, please select "
+                   "another port", port);
+        return -EBUSY;
+    }
+
     pos = pci_add_capability(dev, PCI_CAP_ID_EXP, offset,
                              PCI_EXP_VER2_SIZEOF, errp);
     if (pos < 0) {
-- 
2.41.0