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From:   Aradhya Bhatia <a-bhatia1@ti.com>
To:     Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>
CC:     Devicetree List <devicetree@vger.kernel.org>,
        Linux Kernel List <linux-kernel@vger.kernel.org>,
        Andrew Davis <afd@ti.com>, Nishanth Menon <nm@ti.com>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Devarsh Thakkar <devarsht@ti.com>,
        Jai Luthra <j-luthra@ti.com>,
        Jayesh Choudhary <j-choudhary@ti.com>,
        Aradhya Bhatia <a-bhatia1@ti.com>
Subject: [PATCH] scripts/dtc: Allow ports to have a single port@0 child
Date:   Fri, 13 Oct 2023 14:24:24 +0530
Message-ID: <20231013085424.7137-1-a-bhatia1@ti.com>
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Exempt 'ports' from the rule which asserts that nodes with single child
node having reg = 0, should not have the '#size-cells' and
'#address-cells' properties.

Ports of certain hardware do need to be described as only having a
single child node 'port@0', especially when hardware has multiple ports,
and the other ports 'port@x' are planned to be added subsequently. In
such cases, just using 'port', would be an inaccurate hardware
description.

For example, Texas Instruments' DSS (display-subsystem), which has 2 or
4 video ports depending on the SoC. Describing the first video port with
just 'port' under ports would be inaccurate and even slightly
misleading. Simply using port@0 (when other ports are not added)
produces the following warning, while making dtbs with W=1 flag set[0].

code-block ::

	Warning (graph_child_address): /bus@100000/dss@4a00000/ports:
	graph node has single child node 'port@0',
	#address-cells/#size-cells are not necessary

Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>

[0]: https://lore.kernel.org/all/570903b6-8239-d44a-5fac-71700804cb5d@ti.com/
---
 scripts/dtc/checks.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/scripts/dtc/checks.c b/scripts/dtc/checks.c
index 9f31d2607182..705aa0fbcfa2 100644
--- a/scripts/dtc/checks.c
+++ b/scripts/dtc/checks.c
@@ -1797,9 +1797,18 @@ static void check_graph_child_address(struct check *c, struct dt_info *dti,
 		cnt++;
 	}
 
-	if (cnt == 1 && node->addr_cells != -1)
+	if (cnt == 1 && node->addr_cells != -1) {
+		/*
+		 * The graph node "ports" are exempt from this rule, because
+		 * certain hardware do need to be described as only having a
+		 * signle port with reg = 0.
+		 */
+		if (!strcmp(node->name, "ports"))
+			return;
+
 		FAIL(c, dti, node, "graph node has single child node '%s', #address-cells/#size-cells are not necessary",
 		     node->children->name);
+	}
 }
 WARNING(graph_child_address, check_graph_child_address, NULL, &graph_nodes);
 

base-commit: e3b18f7200f45d66f7141136c25554ac1e82009b
-- 
2.40.1