Re: [PATCH v2 09/10] libfdt: Handle unknown tags on dtb modifications

On Thu, Apr 09, 2026 at 01:54:25PM +0200, Herve Codina wrote:
> The structured tag value definition introduced recently gives the
> ability to ignore unknown tags without any error.
>
> When the dtb is modified those unknown tags have to be taken into
> account.
>
> First, depending on the unknown tag location, the item associated with
> the tag is identified:
>   - An unknown tag located just after a FDT_BEGIN_NODE is related to the
>     node.
>
>   - An unknown tag located just after a FDT_PROP is related to the
>     property.
>
>   - An unknown tag out of any node (i.e located before the first
>     FDT_BEGIN_NODE or after the last FDT_END_NODE) is a global tag
>     related to the dtb itself.
>
> Then, if we are allowed to write a dtb containing unknown tags, the
> following rules are used:
>   - When a property is modified, tags related to this property are
>     removed and the dtb version is downgraded.
>
>   - When a property is removed, tags related to this property are
>     obviously removed. The dtb version is kept unchanged.
>
>   - When a property or a node is added, obviously no unknown tags are
>     added and the dtb version is kept unchanged.
>
>   - When a node is removed, tags related to this node are obviously
>     removed. The dtb version is kept unchanged.
>
>   - Adding, removing or modifying a property is not considered as a node
>     modification and so, those operations have no impacts on unknown
>     tags related to the node. Those node related tags are kept unchanged.
>
>   - The only modification considered as a node modification is setting
>     its name. We consider that this operation has no impact on tags
>     related to the node. Here also, those node related tags and the
>     dtb version are kept unchanged.
>
>   - Global (dtb related) unknown tags are kept unchanged regardless the
>     modification done.
>
> Implement those rules when a dtb is modified.
>
> Signed-off-by: Herve Codina <[email protected]>
> Reviewed-by: Luca Ceresoli <[email protected]>
> ---

Reviewed-by: Frank Li <[email protected]>

>  libfdt/fdt_rw.c                               | 118 +++++++++++++++++-
>  tests/run_tests.sh                            |  50 ++++++++
>  ...own_tags_can_skip.fdtput.test.dtb.0.expect |  31 +++++
>  ...own_tags_can_skip.fdtput.test.dtb.1.expect |  35 ++++++
>  ...own_tags_can_skip.fdtput.test.dtb.2.expect |  33 +++++
>  ...own_tags_can_skip.fdtput.test.dtb.3.expect |  35 ++++++
>  ...own_tags_can_skip.fdtput.test.dtb.4.expect |  34 +++++
>  ...own_tags_can_skip.fdtput.test.dtb.5.expect |  32 +++++
>  ...own_tags_can_skip.fdtput.test.dtb.6.expect |  27 ++++
>  9 files changed, 394 insertions(+), 1 deletion(-)
>  create mode 100644 tests/unknown_tags_can_skip.fdtput.test.dtb.0.expect
>  create mode 100644 tests/unknown_tags_can_skip.fdtput.test.dtb.1.expect
>  create mode 100644 tests/unknown_tags_can_skip.fdtput.test.dtb.2.expect
>  create mode 100644 tests/unknown_tags_can_skip.fdtput.test.dtb.3.expect
>  create mode 100644 tests/unknown_tags_can_skip.fdtput.test.dtb.4.expect
>  create mode 100644 tests/unknown_tags_can_skip.fdtput.test.dtb.5.expect
>  create mode 100644 tests/unknown_tags_can_skip.fdtput.test.dtb.6.expect
>
> diff --git a/libfdt/fdt_rw.c b/libfdt/fdt_rw.c
> index f5c28fc..a8f53b4 100644
> --- a/libfdt/fdt_rw.c
> +++ b/libfdt/fdt_rw.c
> @@ -188,6 +188,60 @@ int fdt_del_mem_rsv(void *fdt, int n)
>  	return fdt_splice_mem_rsv_(fdt, re, 1, 0);
>  }
>
> +static void fdt_nopify_area(void *fdt, int start_offset, int next_offset)
> +{
> +	int count = (next_offset - start_offset) / sizeof(fdt32_t);
> +	fdt32_t fdt32_nop = cpu_to_fdt32(FDT_NOP);
> +	fdt32_t *ptr;
> +
> +	ptr = fdt_offset_ptr_w_(fdt, start_offset);
> +	while (count--)
> +		*(ptr++) = fdt32_nop;
> +};
> +
> +static int fdt_property_remove_unknown_tags(void *fdt,
> +					    const struct fdt_property *prop,
> +					    bool downgrade_version)
> +{
> +	int nextoffset, offset;
> +	bool is_unknown;
> +	uint32_t tag;
> +
> +	tag = fdt_next_tag(fdt, fdt_ptr_offset_(fdt, prop), &nextoffset);
> +	if (tag == FDT_END)
> +		return nextoffset;
> +
> +	/*
> +	 * Look at all tags related to the current property. I.e. tags after the
> +	 * current property and before either the next property, a sub-node  or
> +	 * the end of current node
> +	 */
> +	do {
> +		offset = nextoffset;
> +		tag = fdt_next_tag_(fdt, offset, &nextoffset, &is_unknown);
> +		if (tag == FDT_END)
> +			return nextoffset;
> +
> +		/*
> +		 * Unknown tags are returned as NOP. Force FDT_NOP to be really
> +		 * present in the area to remove the unknown tag and its related
> +		 * data. Also, as a tag is removed, downgrade the dtb version
> +		 * if asked for.
> +		 */
> +		if (tag == FDT_NOP) {
> +			if (is_unknown) {
> +				if (downgrade_version)
> +					fdt_downgrade_version(fdt);
> +				fdt_nopify_area(fdt, offset, nextoffset);
> +			}
> +		}
> +
> +	} while ((tag != FDT_PROP) && (tag != FDT_BEGIN_NODE) &&
> +		 (tag != FDT_END_NODE));
> +
> +	return 0;
> +}
> +
>  static int fdt_resize_property_(void *fdt, int nodeoffset,
>  				const char *name, int namelen,
>  				int len, struct fdt_property **prop)
> @@ -200,6 +254,14 @@ static int fdt_resize_property_(void *fdt, int nodeoffset,
>  	if (!*prop)
>  		return oldlen;
>
> +	/*
> +	 * The property is resized. Remove possible unknown tags related to the
> +	 * property downgrading the dtb version.
> +	 */
> +	err = fdt_property_remove_unknown_tags(fdt, *prop, true);
> +	if (err)
> +		return err;
> +
>  	if ((err = fdt_splice_struct_(fdt, (*prop)->data, FDT_TAGALIGN(oldlen),
>  				      FDT_TAGALIGN(len))))
>  		return err;
> @@ -208,6 +270,29 @@ static int fdt_resize_property_(void *fdt, int nodeoffset,
>  	return 0;
>  }
>
> +static int fdt_node_skip_unknown_tags(void *fdt, int next)
> +{
> +	int nextoffset = next;
> +	int offset;
> +	uint32_t tag;
> +
> +	/*
> +	 * Skip all tags related to the current node. I.e. tags after the
> +	 * current node and before either the next property, a sub-node or the
> +	 * end of current node.
> +	 */
> +	do {
> +		offset = nextoffset;
> +		tag = fdt_next_tag(fdt, offset, &nextoffset);
> +		if (tag == FDT_END)
> +			return nextoffset;
> +
> +	} while ((tag != FDT_PROP) && (tag != FDT_BEGIN_NODE) &&
> +		 (tag != FDT_END_NODE));
> +
> +	return offset;
> +}
> +
>  static int fdt_add_property_(void *fdt, int nodeoffset, const char *name,
>  			     int namelen, int len, struct fdt_property **prop)
>  {
> @@ -220,6 +305,15 @@ static int fdt_add_property_(void *fdt, int nodeoffset, const char *name,
>  	if ((nextoffset = fdt_check_node_offset_(fdt, nodeoffset)) < 0)
>  		return nextoffset;
>
> +	/*
> +	 * nextoffset it at the first tag after the node.
> +	 * Skip possible unknown tags related to the node in order to add the
> +	 * property after those tags.
> +	 */
> +	nextoffset = fdt_node_skip_unknown_tags(fdt, nextoffset);
> +	if (nextoffset < 0)
> +		return nextoffset;
> +
>  	namestroff = fdt_find_add_string_(fdt, name, namelen, &allocated);
>  	if (namestroff < 0)
>  		return namestroff;
> @@ -309,6 +403,14 @@ int fdt_appendprop(void *fdt, int nodeoffset, const char *name,
>
>  	prop = fdt_get_property_w(fdt, nodeoffset, name, &oldlen);
>  	if (prop) {
> +		/*
> +		 * The property is going to be modified. Remove possible unknown
> +		 * tags related to this property downgrading the dtb version.
> +		 */
> +		err = fdt_property_remove_unknown_tags(fdt, prop, true);
> +		if (err)
> +			return err;
> +
>  		newlen = len + oldlen;
>  		err = fdt_splice_struct_(fdt, prop->data,
>  					 FDT_TAGALIGN(oldlen),
> @@ -331,6 +433,7 @@ int fdt_delprop(void *fdt, int nodeoffset, const char *name)
>  {
>  	struct fdt_property *prop;
>  	int len, proplen;
> +	int err;
>
>  	FDT_RW_PROBE(fdt);
>
> @@ -338,6 +441,14 @@ int fdt_delprop(void *fdt, int nodeoffset, const char *name)
>  	if (!prop)
>  		return len;
>
> +	/*
> +	 * The property is going to be removed. Remove also possible unknown
> +	 * tags related to this property. Keep the dtb version unchanged.
> +	 */
> +	err = fdt_property_remove_unknown_tags(fdt, prop, false);
> +	if (err)
> +		return err;
> +
>  	proplen = sizeof(*prop) + FDT_TAGALIGN(len);
>  	return fdt_splice_struct_(fdt, prop, proplen, 0);
>  }
> @@ -366,7 +477,12 @@ int fdt_add_subnode_namelen(void *fdt, int parentoffset,
>  	else if (offset != -FDT_ERR_NOTFOUND)
>  		return offset;
>
> -	/* Try to place the new node after the parent's properties */
> +	/*
> +	 * Try to place the new node after the parent's properties and unknown
> +	 * tags related to those properties.
> +	 * Unknown tags are reported as FDT_NOP tags by fdt_next_tag.
> +	 * Skipping FDT_NOP tags will correctly skip unknown tags.
> +	 */
>  	tag = fdt_next_tag(fdt, parentoffset, &nextoffset);
>  	/* the fdt_subnode_offset_namelen() should ensure this never hits */
>  	if (!can_assume(LIBFDT_FLAWLESS) && (tag != FDT_BEGIN_NODE))
> diff --git a/tests/run_tests.sh b/tests/run_tests.sh
> index 48ac6fa..1ba937d 100755
> --- a/tests/run_tests.sh
> +++ b/tests/run_tests.sh
> @@ -1043,6 +1043,56 @@ fdtput_tests () {
>      run_wrap_error_test $DTPUT $dtb -d /chosen   non-existent-prop
>
>      # TODO: Add tests for verbose mode?
> +
> +    # Modify a dtb containing some "unknown" tags that can be skipped
> +    dtb=unknown_tags_can_skip.fdtput.test.dtb
> +    cp unknown_tags_can_skip.dtb $dtb
> +    base_run_test wrap_fdtdump $dtb $dtb.0.out
> +    # Remove unneeded header fields (keep those related to versions)
> +    sed -i '/^\/.*\(magic\|off\|size\|cpu\)/d' $dtb.0.out
> +    base_run_test check_diff $dtb.0.out "$SRCDIR/$dtb.0.expect"
> +
> +    run_fdtput_test "vwxyz" $dtb / prop-str -ts "vwxyz"
> +    base_run_test wrap_fdtdump $dtb $dtb.1.out
> +    # Remove unneeded header fields (keep those related to versions)
> +    sed -i '/^\/.*\(magic\|off\|size\|cpu\)/d' $dtb.1.out
> +    base_run_test check_diff $dtb.1.out "$SRCDIR/$dtb.1.expect"
> +
> +    cp unknown_tags_can_skip.dtb $dtb
> +    run_wrap_test $DTPUT $dtb -c /tst-fdtput
> +    base_run_test wrap_fdtdump $dtb $dtb.2.out
> +    # Remove unneeded header fields (keep those related to versions)
> +    sed -i '/^\/.*\(magic\|off\|size\|cpu\)/d' $dtb.2.out
> +    base_run_test check_diff $dtb.2.out "$SRCDIR/$dtb.2.expect"
> +    run_wrap_test $DTPUT $dtb -c /tst-fdtput/n1 /tst-fdtput/n2 /tst-fdtput/n3
> +    run_wrap_test $DTPUT $dtb -r /tst-fdtput/n1 /tst-fdtput/n3
> +    run_fdtget_test "n2" $dtb -l  /tst-fdtput
> +    base_run_test wrap_fdtdump $dtb $dtb.3.out
> +    # Remove unneeded header fields (keep those related to versions)
> +    sed -i '/^\/.*\(magic\|off\|size\|cpu\)/d' $dtb.3.out
> +    base_run_test check_diff $dtb.3.out "$SRCDIR/$dtb.3.expect"
> +
> +    cp unknown_tags_can_skip.dtb $dtb
> +    run_wrap_test $DTPUT $dtb -d / prop-str
> +    run_fdtget_test "prop-int" $dtb -p  /
> +    base_run_test wrap_fdtdump $dtb $dtb.4.out
> +    # Remove unneeded header fields (keep those related to versions)
> +    sed -i '/^\/.*\(magic\|off\|size\|cpu\)/d' $dtb.4.out
> +    base_run_test check_diff $dtb.4.out "$SRCDIR/$dtb.4.expect"
> +
> +    cp unknown_tags_can_skip.dtb $dtb
> +    run_wrap_test $DTPUT $dtb /subnode2 prop-tst-fdtput -ts "Test fdtput"
> +    base_run_test wrap_fdtdump $dtb $dtb.5.out
> +    # Remove unneeded header fields (keep those related to versions)
> +    sed -i '/^\/.*\(magic\|off\|size\|cpu\)/d' $dtb.5.out
> +    base_run_test check_diff $dtb.5.out "$SRCDIR/$dtb.5.expect"
> +
> +    cp unknown_tags_can_skip.dtb $dtb
> +    run_wrap_test $DTPUT $dtb -r /subnode2/subsubnode
> +    base_run_test wrap_fdtdump $dtb $dtb.6.out
> +    # Remove unneeded header fields (keep those related to versions)
> +    sed -i '/^\/.*\(magic\|off\|size\|cpu\)/d' $dtb.6.out
> +    base_run_test check_diff $dtb.6.out "$SRCDIR/$dtb.6.expect"
>  }
>
>  utilfdt_tests () {
> diff --git a/tests/unknown_tags_can_skip.fdtput.test.dtb.0.expect b/tests/unknown_tags_can_skip.fdtput.test.dtb.0.expect
> new file mode 100644
> index 0000000..3cdf448
> --- /dev/null
> +++ b/tests/unknown_tags_can_skip.fdtput.test.dtb.0.expect
> @@ -0,0 +1,31 @@
> +/dts-v1/;
> +// version:		4294967295
> +// last_comp_version:	16
> +
> +// Unknown tag ignored: 0xd0000000, data len 4 00000001
> +/ {
> +    // Unknown tag ignored: 0xc0000000, data len 0
> +    prop-int = <0x00003201>;
> +    // Unknown tag ignored: 0xd0000000, data len 4 00000110
> +    prop-str = "abcd";
> +    // Unknown tag ignored: 0xe0000000, data len 8 0000012000000121
> +    // Unknown tag ignored: 0xf0000000, data len 3 101112
> +    subnode1 {
> +        prop-int = <0x00006401 0x00006402>;
> +        // Unknown tag ignored: 0xc0000000, data len 0
> +    };
> +    subnode2 {
> +        // Unknown tag ignored: 0xd0000000, data len 4 00000121
> +        prop-int1 = <0x00064020 0x00064021>;
> +        // Unknown tag ignored: 0xe0000000, data len 8 0000122000001221
> +        prop-int2 = <0x00032022>;
> +        subsubnode {
> +            // Unknown tag ignored: 0xe0000000, data len 8 0000123000001231
> +            prop-int = <0x00064023 0x00064024>;
> +        };
> +        // Unknown tag ignored: 0xf0000000, data len 3 212223
> +    };
> +    // Unknown tag ignored: 0xf0000000, data len 5 3132333435
> +};
> +// Unknown tag ignored: 0xd0000000, data len 4 00000002
> +// Unknown tag ignored: 0xf0000000, data len 2 4041
> diff --git a/tests/unknown_tags_can_skip.fdtput.test.dtb.1.expect b/tests/unknown_tags_can_skip.fdtput.test.dtb.1.expect
> new file mode 100644
> index 0000000..71f2d1c
> --- /dev/null
> +++ b/tests/unknown_tags_can_skip.fdtput.test.dtb.1.expect
> @@ -0,0 +1,35 @@
> +/dts-v1/;
> +// version:		17
> +// last_comp_version:	16
> +
> +// Unknown tag ignored: 0xd0000000, data len 4 00000001
> +/ {
> +    // Unknown tag ignored: 0xc0000000, data len 0
> +    prop-int = <0x00003201>;
> +    // Unknown tag ignored: 0xd0000000, data len 4 00000110
> +    prop-str = "vwxyz";
> +    // [NOP]
> +    // [NOP]
> +    // [NOP]
> +    // [NOP]
> +    // [NOP]
> +    // [NOP]
> +    subnode1 {
> +        prop-int = <0x00006401 0x00006402>;
> +        // Unknown tag ignored: 0xc0000000, data len 0
> +    };
> +    subnode2 {
> +        // Unknown tag ignored: 0xd0000000, data len 4 00000121
> +        prop-int1 = <0x00064020 0x00064021>;
> +        // Unknown tag ignored: 0xe0000000, data len 8 0000122000001221
> +        prop-int2 = <0x00032022>;
> +        subsubnode {
> +            // Unknown tag ignored: 0xe0000000, data len 8 0000123000001231
> +            prop-int = <0x00064023 0x00064024>;
> +        };
> +        // Unknown tag ignored: 0xf0000000, data len 3 212223
> +    };
> +    // Unknown tag ignored: 0xf0000000, data len 5 3132333435
> +};
> +// Unknown tag ignored: 0xd0000000, data len 4 00000002
> +// Unknown tag ignored: 0xf0000000, data len 2 4041
> diff --git a/tests/unknown_tags_can_skip.fdtput.test.dtb.2.expect b/tests/unknown_tags_can_skip.fdtput.test.dtb.2.expect
> new file mode 100644
> index 0000000..bd3a13b
> --- /dev/null
> +++ b/tests/unknown_tags_can_skip.fdtput.test.dtb.2.expect
> @@ -0,0 +1,33 @@
> +/dts-v1/;
> +// version:		17
> +// last_comp_version:	16
> +
> +// Unknown tag ignored: 0xd0000000, data len 4 00000001
> +/ {
> +    // Unknown tag ignored: 0xc0000000, data len 0
> +    prop-int = <0x00003201>;
> +    // Unknown tag ignored: 0xd0000000, data len 4 00000110
> +    prop-str = "abcd";
> +    // Unknown tag ignored: 0xe0000000, data len 8 0000012000000121
> +    // Unknown tag ignored: 0xf0000000, data len 3 101112
> +    tst-fdtput {
> +    };
> +    subnode1 {
> +        prop-int = <0x00006401 0x00006402>;
> +        // Unknown tag ignored: 0xc0000000, data len 0
> +    };
> +    subnode2 {
> +        // Unknown tag ignored: 0xd0000000, data len 4 00000121
> +        prop-int1 = <0x00064020 0x00064021>;
> +        // Unknown tag ignored: 0xe0000000, data len 8 0000122000001221
> +        prop-int2 = <0x00032022>;
> +        subsubnode {
> +            // Unknown tag ignored: 0xe0000000, data len 8 0000123000001231
> +            prop-int = <0x00064023 0x00064024>;
> +        };
> +        // Unknown tag ignored: 0xf0000000, data len 3 212223
> +    };
> +    // Unknown tag ignored: 0xf0000000, data len 5 3132333435
> +};
> +// Unknown tag ignored: 0xd0000000, data len 4 00000002
> +// Unknown tag ignored: 0xf0000000, data len 2 4041
> diff --git a/tests/unknown_tags_can_skip.fdtput.test.dtb.3.expect b/tests/unknown_tags_can_skip.fdtput.test.dtb.3.expect
> new file mode 100644
> index 0000000..237eb95
> --- /dev/null
> +++ b/tests/unknown_tags_can_skip.fdtput.test.dtb.3.expect
> @@ -0,0 +1,35 @@
> +/dts-v1/;
> +// version:		17
> +// last_comp_version:	16
> +
> +// Unknown tag ignored: 0xd0000000, data len 4 00000001
> +/ {
> +    // Unknown tag ignored: 0xc0000000, data len 0
> +    prop-int = <0x00003201>;
> +    // Unknown tag ignored: 0xd0000000, data len 4 00000110
> +    prop-str = "abcd";
> +    // Unknown tag ignored: 0xe0000000, data len 8 0000012000000121
> +    // Unknown tag ignored: 0xf0000000, data len 3 101112
> +    tst-fdtput {
> +        n2 {
> +        };
> +    };
> +    subnode1 {
> +        prop-int = <0x00006401 0x00006402>;
> +        // Unknown tag ignored: 0xc0000000, data len 0
> +    };
> +    subnode2 {
> +        // Unknown tag ignored: 0xd0000000, data len 4 00000121
> +        prop-int1 = <0x00064020 0x00064021>;
> +        // Unknown tag ignored: 0xe0000000, data len 8 0000122000001221
> +        prop-int2 = <0x00032022>;
> +        subsubnode {
> +            // Unknown tag ignored: 0xe0000000, data len 8 0000123000001231
> +            prop-int = <0x00064023 0x00064024>;
> +        };
> +        // Unknown tag ignored: 0xf0000000, data len 3 212223
> +    };
> +    // Unknown tag ignored: 0xf0000000, data len 5 3132333435
> +};
> +// Unknown tag ignored: 0xd0000000, data len 4 00000002
> +// Unknown tag ignored: 0xf0000000, data len 2 4041
> diff --git a/tests/unknown_tags_can_skip.fdtput.test.dtb.4.expect b/tests/unknown_tags_can_skip.fdtput.test.dtb.4.expect
> new file mode 100644
> index 0000000..8473040
> --- /dev/null
> +++ b/tests/unknown_tags_can_skip.fdtput.test.dtb.4.expect
> @@ -0,0 +1,34 @@
> +/dts-v1/;
> +// version:		17
> +// last_comp_version:	16
> +
> +// Unknown tag ignored: 0xd0000000, data len 4 00000001
> +/ {
> +    // Unknown tag ignored: 0xc0000000, data len 0
> +    prop-int = <0x00003201>;
> +    // Unknown tag ignored: 0xd0000000, data len 4 00000110
> +    // [NOP]
> +    // [NOP]
> +    // [NOP]
> +    // [NOP]
> +    // [NOP]
> +    // [NOP]
> +    subnode1 {
> +        prop-int = <0x00006401 0x00006402>;
> +        // Unknown tag ignored: 0xc0000000, data len 0
> +    };
> +    subnode2 {
> +        // Unknown tag ignored: 0xd0000000, data len 4 00000121
> +        prop-int1 = <0x00064020 0x00064021>;
> +        // Unknown tag ignored: 0xe0000000, data len 8 0000122000001221
> +        prop-int2 = <0x00032022>;
> +        subsubnode {
> +            // Unknown tag ignored: 0xe0000000, data len 8 0000123000001231
> +            prop-int = <0x00064023 0x00064024>;
> +        };
> +        // Unknown tag ignored: 0xf0000000, data len 3 212223
> +    };
> +    // Unknown tag ignored: 0xf0000000, data len 5 3132333435
> +};
> +// Unknown tag ignored: 0xd0000000, data len 4 00000002
> +// Unknown tag ignored: 0xf0000000, data len 2 4041
> diff --git a/tests/unknown_tags_can_skip.fdtput.test.dtb.5.expect b/tests/unknown_tags_can_skip.fdtput.test.dtb.5.expect
> new file mode 100644
> index 0000000..f7806f4
> --- /dev/null
> +++ b/tests/unknown_tags_can_skip.fdtput.test.dtb.5.expect
> @@ -0,0 +1,32 @@
> +/dts-v1/;
> +// version:		17
> +// last_comp_version:	16
> +
> +// Unknown tag ignored: 0xd0000000, data len 4 00000001
> +/ {
> +    // Unknown tag ignored: 0xc0000000, data len 0
> +    prop-int = <0x00003201>;
> +    // Unknown tag ignored: 0xd0000000, data len 4 00000110
> +    prop-str = "abcd";
> +    // Unknown tag ignored: 0xe0000000, data len 8 0000012000000121
> +    // Unknown tag ignored: 0xf0000000, data len 3 101112
> +    subnode1 {
> +        prop-int = <0x00006401 0x00006402>;
> +        // Unknown tag ignored: 0xc0000000, data len 0
> +    };
> +    subnode2 {
> +        // Unknown tag ignored: 0xd0000000, data len 4 00000121
> +        prop-tst-fdtput = "Test fdtput";
> +        prop-int1 = <0x00064020 0x00064021>;
> +        // Unknown tag ignored: 0xe0000000, data len 8 0000122000001221
> +        prop-int2 = <0x00032022>;
> +        subsubnode {
> +            // Unknown tag ignored: 0xe0000000, data len 8 0000123000001231
> +            prop-int = <0x00064023 0x00064024>;
> +        };
> +        // Unknown tag ignored: 0xf0000000, data len 3 212223
> +    };
> +    // Unknown tag ignored: 0xf0000000, data len 5 3132333435
> +};
> +// Unknown tag ignored: 0xd0000000, data len 4 00000002
> +// Unknown tag ignored: 0xf0000000, data len 2 4041
> diff --git a/tests/unknown_tags_can_skip.fdtput.test.dtb.6.expect b/tests/unknown_tags_can_skip.fdtput.test.dtb.6.expect
> new file mode 100644
> index 0000000..029f3b4
> --- /dev/null
> +++ b/tests/unknown_tags_can_skip.fdtput.test.dtb.6.expect
> @@ -0,0 +1,27 @@
> +/dts-v1/;
> +// version:		17
> +// last_comp_version:	16
> +
> +// Unknown tag ignored: 0xd0000000, data len 4 00000001
> +/ {
> +    // Unknown tag ignored: 0xc0000000, data len 0
> +    prop-int = <0x00003201>;
> +    // Unknown tag ignored: 0xd0000000, data len 4 00000110
> +    prop-str = "abcd";
> +    // Unknown tag ignored: 0xe0000000, data len 8 0000012000000121
> +    // Unknown tag ignored: 0xf0000000, data len 3 101112
> +    subnode1 {
> +        prop-int = <0x00006401 0x00006402>;
> +        // Unknown tag ignored: 0xc0000000, data len 0
> +    };
> +    subnode2 {
> +        // Unknown tag ignored: 0xd0000000, data len 4 00000121
> +        prop-int1 = <0x00064020 0x00064021>;
> +        // Unknown tag ignored: 0xe0000000, data len 8 0000122000001221
> +        prop-int2 = <0x00032022>;
> +        // Unknown tag ignored: 0xf0000000, data len 3 212223
> +    };
> +    // Unknown tag ignored: 0xf0000000, data len 5 3132333435
> +};
> +// Unknown tag ignored: 0xd0000000, data len 4 00000002
> +// Unknown tag ignored: 0xf0000000, data len 2 4041
> --
> 2.53.0
>