[XS] Change in coreboot[main]: commonlib/device_tree: Return cells properties of parent node

[Julius Werner (Code Review)]

Julius Werner has submitted this change. ( https://review.coreboot.org/c/coreboot/+/85964?usp=email )

Change subject: commonlib/device_tree: Return cells properties of parent node
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commonlib/device_tree: Return cells properties of parent node

In Flattened Device Trees, there exist special properties called
`#address-cells` and `#size-cells` that determine how large addresses
and sizes in `reg` properties are. According to the FDT specification,
each `reg` node cares about the `...cells` property in the _parent_ of
its node. Our current implementation looks for those properties in the
node it finds and returns, which would presumably be the node with the
`reg` property itself. Therefore, we're returning the wrong `...cells`
values.

This isn't really a problem in practice because we also allow inheriting
these properties from the parent when they don't exist in the child, and
nodes that contain `reg` properties usually don't contain `...cells`
properties themselves (because those properties would be incorrect and
useless there), so we usually just end up falling back to the (correct)
value we inherited from the parent. But it's still better to just fix
the mistake, and if we ever happen to have a situation where the node
containing the `reg` property still has children that require different
`...cells` values as well, it could make a difference. (The fact that
we're inheriting these properties is also technically incorrect
according to the spec, but we're doing that intentionally to match
behavior in the Linux kernel.)

This issue was already correctly implemented in the recently added
fdt_find_node() from commit 33079b8174e6 ("lib/device_tree: Add some FDT
helper functions"), and this patch also fixes it in the older
dt_find_node().

Change-Id: I323066477a4d4be17225e0915a81ce2ff39c1e40
Signed-off-by: Julius Werner 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/85964
Reviewed-by: Doug Anderson 
Tested-by: build bot (Jenkins) 
Reviewed-by: Maximilian Brune 
---
M src/commonlib/device_tree.c
1 file changed, 4 insertions(+), 3 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Doug Anderson: Looks good to me, but someone else must approve
  Maximilian Brune: Looks good to me, approved

diff --git a/src/commonlib/device_tree.c b/src/commonlib/device_tree.c
index b2daac9..c73e258 100644
--- a/src/commonlib/device_tree.c
+++ b/src/commonlib/device_tree.c
@@ -1059,12 +1059,13 @@
 {
    struct device_tree_node *node, *found = NULL;

-	/* Update #address-cells and #size-cells for this level. */
-	dt_read_cell_props(parent, addrcp, sizecp);
-
    if (!*path)
    	return parent;

+	/* Update #address-cells and #size-cells for the parent level (cells
+	   properties always count for the direct children of their node). */
+	dt_read_cell_props(parent, addrcp, sizecp);
+
    /* Find the next node in the path, if it exists. */
    list_for_each(node, parent->children, list_node) {
    	if (!strcmp(node->name, *path)) {