linux-kernel - [RFC PATCH 05/15] libfdt: Introduce fdt_first

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Message-ID: <20260210173349.636766-6-herve.codina@bootlin.com>
Date: Tue, 10 Feb 2026 18:33:33 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: David Gibson <david@...son.dropbear.id.au>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>
Cc: Ayush Singh <ayush@...gleboard.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	devicetree-compiler@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	devicetree-spec@...r.kernel.org,
	Hui Pu <hui.pu@...ealthcare.com>,
	Ian Ray <ian.ray@...ealthcare.com>,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Herve Codina <herve.codina@...tlin.com>
Subject: [RFC PATCH 05/15] libfdt: Introduce fdt_first_node()

In several places, libfdt assumes that a FDT_BEGIN_NODE tag is present
at the offset 0 of the structure block.

This assumption is not correct. Indeed, a FDT_NOP can be present at the
offset 0 and this is a legit case.

Introduce fdt_first_node() in order to get the offset of the first node
(first FDT_BEGIN_NODE tag) available in a fdt blob.

Signed-off-by: Herve Codina <herve.codina@...tlin.com>
---
 libfdt/fdt.c             | 25 +++++++++++++++++++++++++
 libfdt/libfdt_internal.h |  1 +
 2 files changed, 26 insertions(+)

diff --git a/libfdt/fdt.c b/libfdt/fdt.c
index 56d4dcb..676c7d7 100644
--- a/libfdt/fdt.c
+++ b/libfdt/fdt.c
@@ -252,6 +252,31 @@ int fdt_check_prop_offset_(const void *fdt, int offset)
 	return offset;
 }
 
+int fdt_first_node(const void *fdt)
+{
+	int nextoffset = 0;
+	int offset;
+	uint32_t tag;
+
+	do {
+		offset = nextoffset;
+		tag = fdt_next_tag(fdt, offset, &nextoffset);
+		switch (tag) {
+		case FDT_END_NODE:
+		case FDT_PROP:
+			return -FDT_ERR_BADSTRUCTURE;
+
+		case FDT_BEGIN_NODE:
+			return offset;
+
+		default:
+			break;
+		}
+	} while (tag != FDT_END);
+
+	return (nextoffset < 0) ? nextoffset : -FDT_ERR_NOTFOUND;
+}
+
 int fdt_next_node(const void *fdt, int offset, int *depth)
 {
 	int nextoffset = 0;
diff --git a/libfdt/libfdt_internal.h b/libfdt/libfdt_internal.h
index 0e103ca..4c15264 100644
--- a/libfdt/libfdt_internal.h
+++ b/libfdt/libfdt_internal.h
@@ -32,6 +32,7 @@ static inline const char *fdt_find_string_(const char *strtab, int tabsize,
 }
 
 int fdt_node_end_offset_(void *fdt, int nodeoffset);
+int fdt_first_node(const void *fdt);
 
 static inline const void *fdt_offset_ptr_(const void *fdt, int offset)
 {
-- 
2.52.0