xen/iommu: Move spin_lock from iommu_dt_device_is_assigned to caller

Rename iommu_dt_device_is_assigned() to iommu_dt_device_is_assigned_locked().

Moving spin_lock to caller was done to prevent the concurrent access to
iommu_dt_device_is_assigned while doing add/remove/assign/deassign. Follow-up
patches in this series introduces node add/remove feature.

Signed-off-by: Vikram Garhwal <vikram.garhwal@amd.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

xen/drivers/passthrough/device_tree.c

@@ -83,16 +83,16 @@ fail:
     return rc;
 }
 
-static bool iommu_dt_device_is_assigned(const struct dt_device_node *dev)
+static bool iommu_dt_device_is_assigned_locked(const struct dt_device_node *dev)
 {
     bool assigned = false;
 
+    ASSERT(spin_is_locked(&dtdevs_lock));
+
     if ( !dt_device_is_protected(dev) )
         return 0;
 
-    spin_lock(&dtdevs_lock);
     assigned = !list_empty(&dev->domain_list);
-    spin_unlock(&dtdevs_lock);
 
     return assigned;
 }
@@ -225,12 +225,16 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct domain *d,
 
         if ( domctl->cmd == XEN_DOMCTL_test_assign_device )
         {
-            if ( iommu_dt_device_is_assigned(dev) )
+            spin_lock(&dtdevs_lock);
+
+            if ( iommu_dt_device_is_assigned_locked(dev) )
             {
                 printk(XENLOG_G_ERR "%s already assigned.\n",
                        dt_node_full_name(dev));
                 ret = -EINVAL;
             }
+
+            spin_unlock(&dtdevs_lock);
             break;
         }