Commit 8f6e2e1e authored by Simon Glass's avatar Simon Glass
Browse files

fdt: Add a function to remove unused strings from a device tree

Property names are stored in a string table. When a node property is
removed, the string table is not updated since other nodes may have a
property with the same name.

Thus it is possible for the string table to build up a number of unused
strings. Add a function to remove these. This works by building a new device
tree from the old one, adding strings one by one as needed.

Signed-off-by: default avatarSimon Glass <>
parent 5b9d44df
......@@ -1646,6 +1646,23 @@ int fdt_del_node(void *fdt, int nodeoffset);
const char *fdt_strerror(int errval);
* fdt_remove_unused_strings() - Remove any unused strings from an FDT
* This creates a new device tree in @new with unused strings removed. The
* called can then use fdt_pack() to minimise the space consumed.
* @old: Old device tree blog
* @new: Place to put new device tree blob, which must be as large as
* @old
* @return
* 0, on success
* -FDT_ERR_BADOFFSET, corrupt device tree
* -FDT_ERR_NOSPACE, out of space, which should not happen unless there
* is something very wrong with the device tree input
int fdt_remove_unused_strings(const void *old, void *new);
struct fdt_region {
int offset;
int size;
......@@ -449,3 +449,35 @@ int fdt_pack(void *fdt)
return 0;
int fdt_remove_unused_strings(const void *old, void *new)
const struct fdt_property *old_prop;
struct fdt_property *new_prop;
int size = fdt_totalsize(old);
int next_offset, offset;
const char *str;
int ret;
int tag = FDT_PROP;
/* Make a copy and remove the strings */
memcpy(new, old, size);
fdt_set_size_dt_strings(new, 0);
/* Add every property name back into the new string table */
for (offset = 0; tag != FDT_END; offset = next_offset) {
tag = fdt_next_tag(old, offset, &next_offset);
if (tag != FDT_PROP)
old_prop = fdt_get_property_by_offset(old, offset, NULL);
new_prop = (struct fdt_property *)(unsigned long)
fdt_get_property_by_offset(new, offset, NULL);
str = fdt_string(old, fdt32_to_cpu(old_prop->nameoff));
ret = _fdt_find_add_string(new, str);
if (ret < 0)
return ret;
new_prop->nameoff = cpu_to_fdt32(ret);
return 0;
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