[PATCH] device-tree: optimize dt_device_for_passthrough()

[Grygorii Strashko <gragst.linux@xxxxxxxxx>]

The dt_device_for_passthrough() is called many times during Xen
initialization and Dom0 creation. On every call it traverses struct
dt_device_node properties list and compares compares properties name with
"xen,passthrough" which is runtime overhead. This can be optimized by
marking dt_device_node as passthrough while unflattening DT.

This patch introduced new struct dt_device_node property "is_passthrough"
which is filled if "xen,passthrough" property is present while unflattening
DT and dt_device_for_passthrough() just return it's value.

Signed-off-by: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
---
 xen/common/device-tree/device-tree.c | 7 +++++--
 xen/include/xen/device_tree.h        | 2 ++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/xen/common/device-tree/device-tree.c 
b/xen/common/device-tree/device-tree.c
index d0528c582565..a329aaf576da 100644
--- a/xen/common/device-tree/device-tree.c
+++ b/xen/common/device-tree/device-tree.c
@@ -1682,8 +1682,7 @@ bool dt_device_is_available(const struct dt_device_node 
*device)
 
 bool dt_device_for_passthrough(const struct dt_device_node *device)
 {
-    return (dt_find_property(device, "xen,passthrough", NULL) != NULL);
-
+    return device->is_passthrough;
 }
 
 static int __dt_parse_phandle_with_args(const struct dt_device_node *np,
@@ -1913,6 +1912,7 @@ static unsigned long unflatten_dt_node(const void *fdt,
         np->used_by = 0;
         /* By default the device is not protected */
         np->is_protected = false;
+        np->is_passthrough = false;
         INIT_LIST_HEAD(&np->domain_list);
 
         if ( new_format )
@@ -2001,6 +2001,9 @@ static unsigned long unflatten_dt_node(const void *fdt,
              * stuff */
             if ( strcmp(pname, "ibm,phandle") == 0 )
                 np->phandle = be32_to_cpup((__be32 *)*p);
+
+            if ( strcmp(pname, "xen,passthrough") == 0 )
+                np->is_passthrough = true;
             pp->name = pname;
             pp->length = sz;
             pp->value = (void *)*p;
diff --git a/xen/include/xen/device_tree.h b/xen/include/xen/device_tree.h
index 5ff763bb80bb..96001d5b7843 100644
--- a/xen/include/xen/device_tree.h
+++ b/xen/include/xen/device_tree.h
@@ -94,6 +94,8 @@ struct dt_device_node {
 
     /* IOMMU specific fields */
     bool is_protected;
+    /* Indicates DT device is for passthrough */
+    bool is_passthrough;
 
 #ifdef CONFIG_STATIC_EVTCHN
     /* HACK: Remove this if there is a need of space */
-- 
2.34.1