Set the vPCI flag in xen_domctl_createdomain to enable vPCI for dom0 if
iommu and PCI passthrough are enabled and there exists a PCI host bridge
in the system.

Adjust pci_host_iterate_bridges_and_count() to count the number of host
bridges if no callback is provided.

Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
---
v3->v4:
* depend on iommu_enabled, pci_passthrough_enabled, and whether there
  is a pci host bridge

v2->v3:
* new patch

[1] https://lists.xenproject.org/archives/html/xen-devel/2023-10/msg00475.html
[2] https://lists.xenproject.org/archives/html/xen-devel/2023-10/msg00210.html
---
 xen/arch/arm/domain_build.c        |  6 ++++++
 xen/arch/arm/include/asm/pci.h     |  9 +++++++++
 xen/arch/arm/pci/pci-host-common.c | 11 ++++++++---
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 49792dd590ee..4750f5c6ad31 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -3915,6 +3915,12 @@ void __init create_dom0(void)
             panic("SVE vector length error\n");
     }
 
+    if ( IS_ENABLED(CONFIG_HAS_VPCI) &&
+         iommu_enabled &&
+         is_pci_passthrough_enabled() &&
+         (pci_host_iterate_bridges_and_count(NULL, NULL) > 0) )
+        dom0_cfg.flags |= XEN_DOMCTL_CDF_vpci;
+
     dom0 = domain_create(0, &dom0_cfg, CDF_privileged | CDF_directmap);
     if ( IS_ERR(dom0) )
         panic("Error creating domain 0 (rc = %ld)\n", PTR_ERR(dom0));
diff --git a/xen/arch/arm/include/asm/pci.h b/xen/arch/arm/include/asm/pci.h
index 8cb46f6b7185..4ae4d8cff8bf 100644
--- a/xen/arch/arm/include/asm/pci.h
+++ b/xen/arch/arm/include/asm/pci.h
@@ -154,5 +154,14 @@ static inline int pci_get_new_domain_nr(void)
     return -1;
 }
 
+struct pci_host_bridge;
+
+static inline int pci_host_iterate_bridges_and_count(
+    struct domain *d,
+    int (*cb)(struct domain *d, struct pci_host_bridge *bridge))
+{
+    return 0;
+}
+
 #endif  /*!CONFIG_HAS_PCI*/
 #endif /* __ARM_PCI_H__ */
diff --git a/xen/arch/arm/pci/pci-host-common.c b/xen/arch/arm/pci/pci-host-common.c
index c0faf0f43675..e6a03ae668f8 100644
--- a/xen/arch/arm/pci/pci-host-common.c
+++ b/xen/arch/arm/pci/pci-host-common.c
@@ -319,9 +319,14 @@ int pci_host_iterate_bridges_and_count(struct domain *d,
     {
         int ret;
 
-        ret = cb(d, bridge);
-        if ( ret < 0 )
-            return ret;
+        if ( cb )
+        {
+            ret = cb(d, bridge);
+            if ( ret < 0 )
+                return ret;
+        }
+        else
+            ret = 1;
         count += ret;
     }
     return count;
-- 
2.42.0