libfdt: fdt_rw: Introduce fdt_downgrade_version()

Current code perform a version downgrade at one place only, the end of
fdt_rw_probe_().

In order to offer a finer grain and choose to downgrade or not depending
on the exact writes done, introduce fdt_downgrade_version() to perform
the downgrade operation.

The modification doesn't introduce any functional changes.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Message-ID: <20260210173349.636766-5-herve.codina@bootlin.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

fdtdump.c

@@ -146,8 +146,7 @@ static void dump_blob(void *blob, bool debug)
 			continue;
 		}
 
-		fprintf(stderr, "%*s ** Unknown tag 0x%08"PRIx32"\n", depth * shift, "", tag);
+		die("** Unknown tag 0x%08"PRIx32"\n", tag);
-		break;
 	}
 }
 

libfdt/fdt_rw.c

@@ -22,6 +22,12 @@ static int fdt_blocks_misordered_(const void *fdt,
 		    (fdt_off_dt_strings(fdt) + fdt_size_dt_strings(fdt)));
 }
 
+static void fdt_downgrade_version(void *fdt)
+{
+	if (!can_assume(LATEST) && fdt_version(fdt) > FDT_LAST_SUPPORTED_VERSION)
+		fdt_set_version(fdt, FDT_LAST_SUPPORTED_VERSION);
+}
+
 static int fdt_rw_probe_(void *fdt)
 {
 	if (can_assume(VALID_DTB))
@@ -33,9 +39,8 @@ static int fdt_rw_probe_(void *fdt)
 	if (fdt_blocks_misordered_(fdt, sizeof(struct fdt_reserve_entry),
 				   fdt_size_dt_struct(fdt)))
 		return -FDT_ERR_BADLAYOUT;
-	if (!can_assume(LATEST) && fdt_version(fdt) > 17)
-		fdt_set_version(fdt, 17);
 
+	fdt_downgrade_version(fdt);
 	return 0;
 }