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>
---
Allowing/enabling vPCI for dom0 on ARM should follow or be part of the
PCI passthrough SMMU series [1]. I'm including it here due to
prerequisites in this Kconfig series. Once the prerequisites are
committed I'll move this patch to the PCI passthrough SMMU series.

v5->v6:
* no change

v4->v5:
* add [FUTURE] tag
* move flags_optional change from the previous patch to here

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/msg00210.html
---
 xen/arch/arm/domain.c              |  3 ++-
 xen/arch/arm/domain_build.c        |  6 ++++++
 xen/arch/arm/include/asm/pci.h     |  9 +++++++++
 xen/arch/arm/pci/pci-host-common.c | 11 ++++++++---
 4 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 28e3aaa5e482..1409a4235e13 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -607,7 +607,8 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
 {
     unsigned int max_vcpus;
     unsigned int flags_required = (XEN_DOMCTL_CDF_hvm | XEN_DOMCTL_CDF_hap);
-    unsigned int flags_optional = (XEN_DOMCTL_CDF_iommu | XEN_DOMCTL_CDF_vpmu);
+    unsigned int flags_optional = (XEN_DOMCTL_CDF_iommu | XEN_DOMCTL_CDF_vpmu |
+                                   XEN_DOMCTL_CDF_vpci);
     unsigned int sve_vl_bits = sve_decode_vl(config->arch.sve_vl);
 
     if ( (config->flags & ~flags_optional) != flags_required )
diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 2dd2926b4144..512b3c4c76e2 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -3916,6 +3916,12 @@ 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 7f77226c9bbf..74816a687bbb 100644
--- a/xen/arch/arm/include/asm/pci.h
+++ b/xen/arch/arm/include/asm/pci.h
@@ -147,5 +147,14 @@ 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