The dtc graph_child_address check can't distinguish between bindings
where there can only be a single endpoint, and cases where there can be
multiple endpoints.
In cases where the bindings allow for multiple endpoints but only one is
described false warnings about unnecessary #address-cells/#size-cells
can be generated, but only if the endpoint described have an address of
0 (A), for single endpoints with a non-zero address (B) no warnings are
generated.
A)
ports {
#address-cells = <1>;
#size-cells = <0>;
port@0 {
#address-cells = <1>;
#size-cells = <0>;
sourceA: endpoint@0 {
reg = <0>
};
};
};
B)
ports {
#address-cells = <1>;
#size-cells = <0>;
port@0 {
#address-cells = <1>;
#size-cells = <0>;
sourceB: endpoint@1 {
reg = <1>
};
};
};
Add a comment in the check to document this.
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
---
Hello,
This was previously part of a patch posted to devicetree@xxxxxxxxxxxxxxx
[1], but as Rob's points out in that thread it should have been posted
separately to devicetree-compiler@xxxxxxxxxxxxxxx. Sorry for not
realising that dtc changes go to thru a separate tree.
1. https://lore.kernel.org/all/20250702085008.689727-1-niklas.soderlund%2Brenesas@xxxxxxxxxxxx/
---
checks.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/checks.c b/checks.c
index 123f2eb425f4..52d09fcf8d3a 100644
--- a/checks.c
+++ b/checks.c
@@ -1913,6 +1913,11 @@ static void check_graph_child_address(struct check *c, struct dt_info *dti,
cnt++;
}
+ /*
+ * This check can produce false warnings if the bindings allow for more
+ * then one endpoint in the node but only one is present and it has a
+ * unit address of zero.
+ */
if (cnt == 1 && node->addr_cells != -1)
FAIL(c, dti, node, "graph node has single child node '%s', #address-cells/#size-cells are not necessary",
node->children->name);
--
2.50.0
