AMD/IOMMU: split amd_iommu_init_one()

Mapping the MMIO space and obtaining feature information needs to happen
slightly earlier, such that for x2APIC support we can set XTEn prior to
calling amd_iommu_update_ivrs_mapping_acpi() and
amd_iommu_setup_ioapic_remapping().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Brian Woods <brian.woods@xxxxxxx>

--- a/xen/drivers/passthrough/amd/iommu_init.c
+++ b/xen/drivers/passthrough/amd/iommu_init.c
@@ -969,14 +969,6 @@ static void * __init allocate_ppr_log(st
 
 static int __init amd_iommu_init_one(struct amd_iommu *iommu)
 {
-    if ( map_iommu_mmio_region(iommu) != 0 )
-        goto error_out;
-
-    get_iommu_features(iommu);
-
-    if ( iommu->features.raw )
-        iommuv2_enabled = 1;
-
     if ( allocate_cmd_buffer(iommu) == NULL )
         goto error_out;
 
@@ -1201,6 +1193,23 @@ static bool_t __init amd_sp5100_erratum2
     return 0;
 }
 
+static int __init amd_iommu_prepare_one(struct amd_iommu *iommu)
+{
+    int rc = alloc_ivrs_mappings(iommu->seg);
+
+    if ( !rc )
+        rc = map_iommu_mmio_region(iommu);
+    if ( rc )
+        return rc;
+
+    get_iommu_features(iommu);
+
+    if ( iommu->features.raw )
+        iommuv2_enabled = true;
+
+    return 0;
+}
+
 int __init amd_iommu_init(void)
 {
     struct amd_iommu *iommu;
@@ -1231,7 +1240,7 @@ int __init amd_iommu_init(void)
     radix_tree_init(&ivrs_maps);
     for_each_amd_iommu ( iommu )
     {
-        rc = alloc_ivrs_mappings(iommu->seg);
+        rc = amd_iommu_prepare_one(iommu);
         if ( rc )
             goto error_out;
     }