Hi,

On 16/08/2019 00:36, Stefano Stabellini wrote:
Add a new parameter to device_tree_for_each_node: node, the node to
start the search from. Passing 0 triggers the old behavior.

Here you say 0 triggers the old behavior but...


Set min_depth to depth of the current node + 1 to avoid scanning
siblings of the initial node passed as an argument.

Don't call func() on the parent node passed as an argument. Clarify the
change in the comment on top of the function.

... here you mention that the first node will be skipped. So the behavior is now different and should be explained in the commit message why this is fine to skip the root node.


Signed-off-by: Stefano Stabellini <stefa...@xilinx.com>
---
Changes in v6:
- fix code style
- don't call func() on the first node

Changes in v5:
- go back to v3
- code style improvement in acpi/boot.c
- improve comments and commit message
- increase min_depth to avoid parsing siblings
- replace for with do/while loop and increase min_depth to avoid
   scanning siblings of the initial node
- pass only node, calculate depth

Changes in v3:
- improve commit message
- improve in-code comments
- improve code style

Changes in v2:
- new
---
  xen/arch/arm/acpi/boot.c      |  8 +++++---
  xen/arch/arm/bootfdt.c        | 34 ++++++++++++++++++++--------------
  xen/include/xen/device_tree.h |  6 +++---
  3 files changed, 28 insertions(+), 20 deletions(-)

diff --git a/xen/arch/arm/acpi/boot.c b/xen/arch/arm/acpi/boot.c
index 9b29769a10..bf9c78b02c 100644
--- a/xen/arch/arm/acpi/boot.c
+++ b/xen/arch/arm/acpi/boot.c
@@ -246,9 +246,11 @@ int __init acpi_boot_table_init(void)
       * - the device tree is not empty (it has more than just a /chosen node)
       *   and ACPI has not been force enabled (acpi=force)
       */
-    if ( param_acpi_off || ( !param_acpi_force
-                             && 
device_tree_for_each_node(device_tree_flattened,
-                                                   dt_scan_depth1_nodes, 
NULL)))
+    if ( param_acpi_off)
+        goto disable;
+    if ( !param_acpi_force &&
+         device_tree_for_each_node(device_tree_flattened, 0,
+                                   dt_scan_depth1_nodes, NULL) )
          goto disable;
/*
diff --git a/xen/arch/arm/bootfdt.c b/xen/arch/arm/bootfdt.c
index 891b4b66ff..f1614ef7fc 100644
--- a/xen/arch/arm/bootfdt.c
+++ b/xen/arch/arm/bootfdt.c
@@ -75,9 +75,10 @@ static u32 __init device_tree_get_u32(const void *fdt, int 
node,
  }
/**
- * device_tree_for_each_node - iterate over all device tree nodes
+ * device_tree_for_each_node - iterate over all device tree sub-nodes
   * @fdt: flat device tree.
- * @func: function to call for each node.
+ * @node: parent node to start the search from
+ * @func: function to call for each sub-node.
   * @data: data to pass to @func.
   *
   * Any nodes nested at DEVICE_TREE_MAX_DEPTH or deeper are ignored.
@@ -85,20 +86,18 @@ static u32 __init device_tree_get_u32(const void *fdt, int 
node,
   * Returns 0 if all nodes were iterated over successfully.  If @func
   * returns a value different from 0, that value is returned immediately.
   */
-int __init device_tree_for_each_node(const void *fdt,
+int __init device_tree_for_each_node(const void *fdt, int node,
                                       device_tree_node_func func,
                                       void *data)
  {
-    int node;
-    int depth;
+    int depth = fdt_node_depth(fdt, node);

Sorry I didn't spot this in the previous version. As I pointed out on v4 (and you actually agreed!), you don't need the absolute depth...

You only need the relative depth. So this is a waste of processing as you have to go through the FDT to calculate the depth.

This is not entirely critical so I would be willing to consider a patch on top of this series.

+    int min_depth = depth + 1;
+    int first_node = node;

NIT: Anything that can't change should really be const to catch any mistake.

      u32 address_cells[DEVICE_TREE_MAX_DEPTH];
      u32 size_cells[DEVICE_TREE_MAX_DEPTH];
      int ret;
- for ( node = 0, depth = 0;
-          node >=0 && depth >= 0;
-          node = fdt_next_node(fdt, node, &depth) )
-    {
+    do {
          const char *name = fdt_get_name(fdt, node, NULL);
          u32 as, ss;
@@ -117,10 +116,17 @@ int __init device_tree_for_each_node(const void *fdt,
          size_cells[depth] = device_tree_get_u32(fdt, node,
                                                  "#size-cells", ss);
- ret = func(fdt, node, name, depth, as, ss, data);
-        if ( ret != 0 )
-            return ret;
-    }
+        /* skip the first node */
+        if ( node != first_node )
+        {
+            ret = func(fdt, node, name, depth, as, ss, data);
+            if ( ret != 0 )
+                return ret;
+        }
+
+        node = fdt_next_node(fdt, node, &depth);
+    } while ( node >= 0 && depth >= min_depth );
+
      return 0;
  }
@@ -357,7 +363,7 @@ size_t __init boot_fdt_info(const void *fdt, paddr_t paddr) add_boot_module(BOOTMOD_FDT, paddr, fdt_totalsize(fdt), false); - device_tree_for_each_node((void *)fdt, early_scan_node, NULL);
+    device_tree_for_each_node((void *)fdt, 0, early_scan_node, NULL);
      early_print_info();
return fdt_totalsize(fdt);
diff --git a/xen/include/xen/device_tree.h b/xen/include/xen/device_tree.h
index 83156297e2..9a7a8f2dab 100644
--- a/xen/include/xen/device_tree.h
+++ b/xen/include/xen/device_tree.h
@@ -158,9 +158,9 @@ typedef int (*device_tree_node_func)(const void *fdt,
extern const void *device_tree_flattened; -int device_tree_for_each_node(const void *fdt,
-                                     device_tree_node_func func,
-                                     void *data);
+int device_tree_for_each_node(const void *fdt, int node,
+                              device_tree_node_func func,
+                              void *data);
/**
   * dt_unflatten_host_device_tree - Unflatten the host device tree


Cheers,

--
Julien Grall

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