hw/pci-bridge/pcie_pci_bridge: properly handle MSI unavailability case

QEMU with the pcie-pci-bridge device crashes if the guest board doesn't support MSI,
e.g. 'qemu-system-ppc64 -M prep -device pcie-pci-bridge'.
This is caused by wrong pcie-pci-bridge instantiation error handling. This patch fixes this issue
by falling back to legacy INTx if MSI is not available.
Also set the bridge's 'msi' property default value to 'auto' in order to trigger errors
only when user explicitly set msi=on.
Reported-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NAleksandr Bezzubikov <zuban32s@gmail.com>
Reviewed-by: NMarcel Apfelbaum <marcel@redhat.com>
Tested-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/pci-bridge/pcie_pci_bridge.c

@@ -65,10 +65,18 @@ static void pcie_pci_bridge_realize(PCIDevice *d, Error **errp)
         goto aer_error;
     }
 
+    Error *local_err = NULL;
     if (pcie_br->msi != ON_OFF_AUTO_OFF) {
-        rc = msi_init(d, 0, 1, true, true, errp);
+        rc = msi_init(d, 0, 1, true, true, &local_err);
         if (rc < 0) {
-            goto msi_error;
+            assert(rc == -ENOTSUP);
+            if (pcie_br->msi != ON_OFF_AUTO_ON) {
+                error_free(local_err);
+            } else {
+                /* failed to satisfy user's explicit request for MSI */
+                error_propagate(errp, local_err);
+                goto msi_error;
+            }
         }
     }
     pci_register_bar(d, 0, PCI_BASE_ADDRESS_SPACE_MEMORY |
@@ -81,7 +89,7 @@ aer_error:
 pm_error:
     pcie_cap_exit(d);
 cap_error:
-    shpc_free(d);
+    shpc_cleanup(d, &pcie_br->shpc_bar);
 error:
     pci_bridge_exitfn(d);
 }
@@ -98,7 +106,9 @@ static void pcie_pci_bridge_reset(DeviceState *qdev)
 {
     PCIDevice *d = PCI_DEVICE(qdev);
     pci_bridge_reset(qdev);
-    msi_reset(d);
+    if (msi_present(d)) {
+        msi_reset(d);
+    }
     shpc_reset(d);
 }
 
@@ -106,12 +116,14 @@ static void pcie_pci_bridge_write_config(PCIDevice *d,
         uint32_t address, uint32_t val, int len)
 {
     pci_bridge_write_config(d, address, val, len);
-    msi_write_config(d, address, val, len);
+    if (msi_present(d)) {
+        msi_write_config(d, address, val, len);
+    }
     shpc_cap_write_config(d, address, val, len);
 }
 
 static Property pcie_pci_bridge_dev_properties[] = {
-        DEFINE_PROP_ON_OFF_AUTO("msi", PCIEPCIBridge, msi, ON_OFF_AUTO_ON),
+        DEFINE_PROP_ON_OFF_AUTO("msi", PCIEPCIBridge, msi, ON_OFF_AUTO_AUTO),
         DEFINE_PROP_END_OF_LIST(),
 };