xref: /linux/scripts/dtc/libfdt/fdt_overlay.c (revision 2da68a77)
1 // SPDX-License-Identifier: (GPL-2.0-or-later OR BSD-2-Clause)
2 /*
3  * libfdt - Flat Device Tree manipulation
4  * Copyright (C) 2016 Free Electrons
5  * Copyright (C) 2016 NextThing Co.
6  */
7 #include "libfdt_env.h"
8 
9 #include <fdt.h>
10 #include <libfdt.h>
11 
12 #include "libfdt_internal.h"
13 
14 /**
15  * overlay_get_target_phandle - retrieves the target phandle of a fragment
16  * @fdto: pointer to the device tree overlay blob
17  * @fragment: node offset of the fragment in the overlay
18  *
19  * overlay_get_target_phandle() retrieves the target phandle of an
20  * overlay fragment when that fragment uses a phandle (target
21  * property) instead of a path (target-path property).
22  *
23  * returns:
24  *      the phandle pointed by the target property
25  *      0, if the phandle was not found
26  *	-1, if the phandle was malformed
27  */
28 static uint32_t overlay_get_target_phandle(const void *fdto, int fragment)
29 {
30 	const fdt32_t *val;
31 	int len;
32 
33 	val = fdt_getprop(fdto, fragment, "target", &len);
34 	if (!val)
35 		return 0;
36 
37 	if ((len != sizeof(*val)) || (fdt32_to_cpu(*val) == (uint32_t)-1))
38 		return (uint32_t)-1;
39 
40 	return fdt32_to_cpu(*val);
41 }
42 
43 /**
44  * overlay_get_target - retrieves the offset of a fragment's target
45  * @fdt: Base device tree blob
46  * @fdto: Device tree overlay blob
47  * @fragment: node offset of the fragment in the overlay
48  * @pathp: pointer which receives the path of the target (or NULL)
49  *
50  * overlay_get_target() retrieves the target offset in the base
51  * device tree of a fragment, no matter how the actual targeting is
52  * done (through a phandle or a path)
53  *
54  * returns:
55  *      the targeted node offset in the base device tree
56  *      Negative error code on error
57  */
58 static int overlay_get_target(const void *fdt, const void *fdto,
59 			      int fragment, char const **pathp)
60 {
61 	uint32_t phandle;
62 	const char *path = NULL;
63 	int path_len = 0, ret;
64 
65 	/* Try first to do a phandle based lookup */
66 	phandle = overlay_get_target_phandle(fdto, fragment);
67 	if (phandle == (uint32_t)-1)
68 		return -FDT_ERR_BADPHANDLE;
69 
70 	/* no phandle, try path */
71 	if (!phandle) {
72 		/* And then a path based lookup */
73 		path = fdt_getprop(fdto, fragment, "target-path", &path_len);
74 		if (path)
75 			ret = fdt_path_offset(fdt, path);
76 		else
77 			ret = path_len;
78 	} else
79 		ret = fdt_node_offset_by_phandle(fdt, phandle);
80 
81 	/*
82 	* If we haven't found either a target or a
83 	* target-path property in a node that contains a
84 	* __overlay__ subnode (we wouldn't be called
85 	* otherwise), consider it a improperly written
86 	* overlay
87 	*/
88 	if (ret < 0 && path_len == -FDT_ERR_NOTFOUND)
89 		ret = -FDT_ERR_BADOVERLAY;
90 
91 	/* return on error */
92 	if (ret < 0)
93 		return ret;
94 
95 	/* return pointer to path (if available) */
96 	if (pathp)
97 		*pathp = path ? path : NULL;
98 
99 	return ret;
100 }
101 
102 /**
103  * overlay_phandle_add_offset - Increases a phandle by an offset
104  * @fdt: Base device tree blob
105  * @node: Device tree overlay blob
106  * @name: Name of the property to modify (phandle or linux,phandle)
107  * @delta: offset to apply
108  *
109  * overlay_phandle_add_offset() increments a node phandle by a given
110  * offset.
111  *
112  * returns:
113  *      0 on success.
114  *      Negative error code on error
115  */
116 static int overlay_phandle_add_offset(void *fdt, int node,
117 				      const char *name, uint32_t delta)
118 {
119 	const fdt32_t *val;
120 	uint32_t adj_val;
121 	int len;
122 
123 	val = fdt_getprop(fdt, node, name, &len);
124 	if (!val)
125 		return len;
126 
127 	if (len != sizeof(*val))
128 		return -FDT_ERR_BADPHANDLE;
129 
130 	adj_val = fdt32_to_cpu(*val);
131 	if ((adj_val + delta) < adj_val)
132 		return -FDT_ERR_NOPHANDLES;
133 
134 	adj_val += delta;
135 	if (adj_val == (uint32_t)-1)
136 		return -FDT_ERR_NOPHANDLES;
137 
138 	return fdt_setprop_inplace_u32(fdt, node, name, adj_val);
139 }
140 
141 /**
142  * overlay_adjust_node_phandles - Offsets the phandles of a node
143  * @fdto: Device tree overlay blob
144  * @node: Offset of the node we want to adjust
145  * @delta: Offset to shift the phandles of
146  *
147  * overlay_adjust_node_phandles() adds a constant to all the phandles
148  * of a given node. This is mainly use as part of the overlay
149  * application process, when we want to update all the overlay
150  * phandles to not conflict with the overlays of the base device tree.
151  *
152  * returns:
153  *      0 on success
154  *      Negative error code on failure
155  */
156 static int overlay_adjust_node_phandles(void *fdto, int node,
157 					uint32_t delta)
158 {
159 	int child;
160 	int ret;
161 
162 	ret = overlay_phandle_add_offset(fdto, node, "phandle", delta);
163 	if (ret && ret != -FDT_ERR_NOTFOUND)
164 		return ret;
165 
166 	ret = overlay_phandle_add_offset(fdto, node, "linux,phandle", delta);
167 	if (ret && ret != -FDT_ERR_NOTFOUND)
168 		return ret;
169 
170 	fdt_for_each_subnode(child, fdto, node) {
171 		ret = overlay_adjust_node_phandles(fdto, child, delta);
172 		if (ret)
173 			return ret;
174 	}
175 
176 	return 0;
177 }
178 
179 /**
180  * overlay_adjust_local_phandles - Adjust the phandles of a whole overlay
181  * @fdto: Device tree overlay blob
182  * @delta: Offset to shift the phandles of
183  *
184  * overlay_adjust_local_phandles() adds a constant to all the
185  * phandles of an overlay. This is mainly use as part of the overlay
186  * application process, when we want to update all the overlay
187  * phandles to not conflict with the overlays of the base device tree.
188  *
189  * returns:
190  *      0 on success
191  *      Negative error code on failure
192  */
193 static int overlay_adjust_local_phandles(void *fdto, uint32_t delta)
194 {
195 	/*
196 	 * Start adjusting the phandles from the overlay root
197 	 */
198 	return overlay_adjust_node_phandles(fdto, 0, delta);
199 }
200 
201 /**
202  * overlay_update_local_node_references - Adjust the overlay references
203  * @fdto: Device tree overlay blob
204  * @tree_node: Node offset of the node to operate on
205  * @fixup_node: Node offset of the matching local fixups node
206  * @delta: Offset to shift the phandles of
207  *
208  * overlay_update_local_nodes_references() update the phandles
209  * pointing to a node within the device tree overlay by adding a
210  * constant delta.
211  *
212  * This is mainly used as part of a device tree application process,
213  * where you want the device tree overlays phandles to not conflict
214  * with the ones from the base device tree before merging them.
215  *
216  * returns:
217  *      0 on success
218  *      Negative error code on failure
219  */
220 static int overlay_update_local_node_references(void *fdto,
221 						int tree_node,
222 						int fixup_node,
223 						uint32_t delta)
224 {
225 	int fixup_prop;
226 	int fixup_child;
227 	int ret;
228 
229 	fdt_for_each_property_offset(fixup_prop, fdto, fixup_node) {
230 		const fdt32_t *fixup_val;
231 		const char *tree_val;
232 		const char *name;
233 		int fixup_len;
234 		int tree_len;
235 		int i;
236 
237 		fixup_val = fdt_getprop_by_offset(fdto, fixup_prop,
238 						  &name, &fixup_len);
239 		if (!fixup_val)
240 			return fixup_len;
241 
242 		if (fixup_len % sizeof(uint32_t))
243 			return -FDT_ERR_BADOVERLAY;
244 		fixup_len /= sizeof(uint32_t);
245 
246 		tree_val = fdt_getprop(fdto, tree_node, name, &tree_len);
247 		if (!tree_val) {
248 			if (tree_len == -FDT_ERR_NOTFOUND)
249 				return -FDT_ERR_BADOVERLAY;
250 
251 			return tree_len;
252 		}
253 
254 		for (i = 0; i < fixup_len; i++) {
255 			fdt32_t adj_val;
256 			uint32_t poffset;
257 
258 			poffset = fdt32_to_cpu(fixup_val[i]);
259 
260 			/*
261 			 * phandles to fixup can be unaligned.
262 			 *
263 			 * Use a memcpy for the architectures that do
264 			 * not support unaligned accesses.
265 			 */
266 			memcpy(&adj_val, tree_val + poffset, sizeof(adj_val));
267 
268 			adj_val = cpu_to_fdt32(fdt32_to_cpu(adj_val) + delta);
269 
270 			ret = fdt_setprop_inplace_namelen_partial(fdto,
271 								  tree_node,
272 								  name,
273 								  strlen(name),
274 								  poffset,
275 								  &adj_val,
276 								  sizeof(adj_val));
277 			if (ret == -FDT_ERR_NOSPACE)
278 				return -FDT_ERR_BADOVERLAY;
279 
280 			if (ret)
281 				return ret;
282 		}
283 	}
284 
285 	fdt_for_each_subnode(fixup_child, fdto, fixup_node) {
286 		const char *fixup_child_name = fdt_get_name(fdto, fixup_child,
287 							    NULL);
288 		int tree_child;
289 
290 		tree_child = fdt_subnode_offset(fdto, tree_node,
291 						fixup_child_name);
292 		if (tree_child == -FDT_ERR_NOTFOUND)
293 			return -FDT_ERR_BADOVERLAY;
294 		if (tree_child < 0)
295 			return tree_child;
296 
297 		ret = overlay_update_local_node_references(fdto,
298 							   tree_child,
299 							   fixup_child,
300 							   delta);
301 		if (ret)
302 			return ret;
303 	}
304 
305 	return 0;
306 }
307 
308 /**
309  * overlay_update_local_references - Adjust the overlay references
310  * @fdto: Device tree overlay blob
311  * @delta: Offset to shift the phandles of
312  *
313  * overlay_update_local_references() update all the phandles pointing
314  * to a node within the device tree overlay by adding a constant
315  * delta to not conflict with the base overlay.
316  *
317  * This is mainly used as part of a device tree application process,
318  * where you want the device tree overlays phandles to not conflict
319  * with the ones from the base device tree before merging them.
320  *
321  * returns:
322  *      0 on success
323  *      Negative error code on failure
324  */
325 static int overlay_update_local_references(void *fdto, uint32_t delta)
326 {
327 	int fixups;
328 
329 	fixups = fdt_path_offset(fdto, "/__local_fixups__");
330 	if (fixups < 0) {
331 		/* There's no local phandles to adjust, bail out */
332 		if (fixups == -FDT_ERR_NOTFOUND)
333 			return 0;
334 
335 		return fixups;
336 	}
337 
338 	/*
339 	 * Update our local references from the root of the tree
340 	 */
341 	return overlay_update_local_node_references(fdto, 0, fixups,
342 						    delta);
343 }
344 
345 /**
346  * overlay_fixup_one_phandle - Set an overlay phandle to the base one
347  * @fdt: Base Device Tree blob
348  * @fdto: Device tree overlay blob
349  * @symbols_off: Node offset of the symbols node in the base device tree
350  * @path: Path to a node holding a phandle in the overlay
351  * @path_len: number of path characters to consider
352  * @name: Name of the property holding the phandle reference in the overlay
353  * @name_len: number of name characters to consider
354  * @poffset: Offset within the overlay property where the phandle is stored
355  * @label: Label of the node referenced by the phandle
356  *
357  * overlay_fixup_one_phandle() resolves an overlay phandle pointing to
358  * a node in the base device tree.
359  *
360  * This is part of the device tree overlay application process, when
361  * you want all the phandles in the overlay to point to the actual
362  * base dt nodes.
363  *
364  * returns:
365  *      0 on success
366  *      Negative error code on failure
367  */
368 static int overlay_fixup_one_phandle(void *fdt, void *fdto,
369 				     int symbols_off,
370 				     const char *path, uint32_t path_len,
371 				     const char *name, uint32_t name_len,
372 				     int poffset, const char *label)
373 {
374 	const char *symbol_path;
375 	uint32_t phandle;
376 	fdt32_t phandle_prop;
377 	int symbol_off, fixup_off;
378 	int prop_len;
379 
380 	if (symbols_off < 0)
381 		return symbols_off;
382 
383 	symbol_path = fdt_getprop(fdt, symbols_off, label,
384 				  &prop_len);
385 	if (!symbol_path)
386 		return prop_len;
387 
388 	symbol_off = fdt_path_offset(fdt, symbol_path);
389 	if (symbol_off < 0)
390 		return symbol_off;
391 
392 	phandle = fdt_get_phandle(fdt, symbol_off);
393 	if (!phandle)
394 		return -FDT_ERR_NOTFOUND;
395 
396 	fixup_off = fdt_path_offset_namelen(fdto, path, path_len);
397 	if (fixup_off == -FDT_ERR_NOTFOUND)
398 		return -FDT_ERR_BADOVERLAY;
399 	if (fixup_off < 0)
400 		return fixup_off;
401 
402 	phandle_prop = cpu_to_fdt32(phandle);
403 	return fdt_setprop_inplace_namelen_partial(fdto, fixup_off,
404 						   name, name_len, poffset,
405 						   &phandle_prop,
406 						   sizeof(phandle_prop));
407 };
408 
409 /**
410  * overlay_fixup_phandle - Set an overlay phandle to the base one
411  * @fdt: Base Device Tree blob
412  * @fdto: Device tree overlay blob
413  * @symbols_off: Node offset of the symbols node in the base device tree
414  * @property: Property offset in the overlay holding the list of fixups
415  *
416  * overlay_fixup_phandle() resolves all the overlay phandles pointed
417  * to in a __fixups__ property, and updates them to match the phandles
418  * in use in the base device tree.
419  *
420  * This is part of the device tree overlay application process, when
421  * you want all the phandles in the overlay to point to the actual
422  * base dt nodes.
423  *
424  * returns:
425  *      0 on success
426  *      Negative error code on failure
427  */
428 static int overlay_fixup_phandle(void *fdt, void *fdto, int symbols_off,
429 				 int property)
430 {
431 	const char *value;
432 	const char *label;
433 	int len;
434 
435 	value = fdt_getprop_by_offset(fdto, property,
436 				      &label, &len);
437 	if (!value) {
438 		if (len == -FDT_ERR_NOTFOUND)
439 			return -FDT_ERR_INTERNAL;
440 
441 		return len;
442 	}
443 
444 	do {
445 		const char *path, *name, *fixup_end;
446 		const char *fixup_str = value;
447 		uint32_t path_len, name_len;
448 		uint32_t fixup_len;
449 		char *sep, *endptr;
450 		int poffset, ret;
451 
452 		fixup_end = memchr(value, '\0', len);
453 		if (!fixup_end)
454 			return -FDT_ERR_BADOVERLAY;
455 		fixup_len = fixup_end - fixup_str;
456 
457 		len -= fixup_len + 1;
458 		value += fixup_len + 1;
459 
460 		path = fixup_str;
461 		sep = memchr(fixup_str, ':', fixup_len);
462 		if (!sep || *sep != ':')
463 			return -FDT_ERR_BADOVERLAY;
464 
465 		path_len = sep - path;
466 		if (path_len == (fixup_len - 1))
467 			return -FDT_ERR_BADOVERLAY;
468 
469 		fixup_len -= path_len + 1;
470 		name = sep + 1;
471 		sep = memchr(name, ':', fixup_len);
472 		if (!sep || *sep != ':')
473 			return -FDT_ERR_BADOVERLAY;
474 
475 		name_len = sep - name;
476 		if (!name_len)
477 			return -FDT_ERR_BADOVERLAY;
478 
479 		poffset = strtoul(sep + 1, &endptr, 10);
480 		if ((*endptr != '\0') || (endptr <= (sep + 1)))
481 			return -FDT_ERR_BADOVERLAY;
482 
483 		ret = overlay_fixup_one_phandle(fdt, fdto, symbols_off,
484 						path, path_len, name, name_len,
485 						poffset, label);
486 		if (ret)
487 			return ret;
488 	} while (len > 0);
489 
490 	return 0;
491 }
492 
493 /**
494  * overlay_fixup_phandles - Resolve the overlay phandles to the base
495  *                          device tree
496  * @fdt: Base Device Tree blob
497  * @fdto: Device tree overlay blob
498  *
499  * overlay_fixup_phandles() resolves all the overlay phandles pointing
500  * to nodes in the base device tree.
501  *
502  * This is one of the steps of the device tree overlay application
503  * process, when you want all the phandles in the overlay to point to
504  * the actual base dt nodes.
505  *
506  * returns:
507  *      0 on success
508  *      Negative error code on failure
509  */
510 static int overlay_fixup_phandles(void *fdt, void *fdto)
511 {
512 	int fixups_off, symbols_off;
513 	int property;
514 
515 	/* We can have overlays without any fixups */
516 	fixups_off = fdt_path_offset(fdto, "/__fixups__");
517 	if (fixups_off == -FDT_ERR_NOTFOUND)
518 		return 0; /* nothing to do */
519 	if (fixups_off < 0)
520 		return fixups_off;
521 
522 	/* And base DTs without symbols */
523 	symbols_off = fdt_path_offset(fdt, "/__symbols__");
524 	if ((symbols_off < 0 && (symbols_off != -FDT_ERR_NOTFOUND)))
525 		return symbols_off;
526 
527 	fdt_for_each_property_offset(property, fdto, fixups_off) {
528 		int ret;
529 
530 		ret = overlay_fixup_phandle(fdt, fdto, symbols_off, property);
531 		if (ret)
532 			return ret;
533 	}
534 
535 	return 0;
536 }
537 
538 /**
539  * overlay_apply_node - Merges a node into the base device tree
540  * @fdt: Base Device Tree blob
541  * @target: Node offset in the base device tree to apply the fragment to
542  * @fdto: Device tree overlay blob
543  * @node: Node offset in the overlay holding the changes to merge
544  *
545  * overlay_apply_node() merges a node into a target base device tree
546  * node pointed.
547  *
548  * This is part of the final step in the device tree overlay
549  * application process, when all the phandles have been adjusted and
550  * resolved and you just have to merge overlay into the base device
551  * tree.
552  *
553  * returns:
554  *      0 on success
555  *      Negative error code on failure
556  */
557 static int overlay_apply_node(void *fdt, int target,
558 			      void *fdto, int node)
559 {
560 	int property;
561 	int subnode;
562 
563 	fdt_for_each_property_offset(property, fdto, node) {
564 		const char *name;
565 		const void *prop;
566 		int prop_len;
567 		int ret;
568 
569 		prop = fdt_getprop_by_offset(fdto, property, &name,
570 					     &prop_len);
571 		if (prop_len == -FDT_ERR_NOTFOUND)
572 			return -FDT_ERR_INTERNAL;
573 		if (prop_len < 0)
574 			return prop_len;
575 
576 		ret = fdt_setprop(fdt, target, name, prop, prop_len);
577 		if (ret)
578 			return ret;
579 	}
580 
581 	fdt_for_each_subnode(subnode, fdto, node) {
582 		const char *name = fdt_get_name(fdto, subnode, NULL);
583 		int nnode;
584 		int ret;
585 
586 		nnode = fdt_add_subnode(fdt, target, name);
587 		if (nnode == -FDT_ERR_EXISTS) {
588 			nnode = fdt_subnode_offset(fdt, target, name);
589 			if (nnode == -FDT_ERR_NOTFOUND)
590 				return -FDT_ERR_INTERNAL;
591 		}
592 
593 		if (nnode < 0)
594 			return nnode;
595 
596 		ret = overlay_apply_node(fdt, nnode, fdto, subnode);
597 		if (ret)
598 			return ret;
599 	}
600 
601 	return 0;
602 }
603 
604 /**
605  * overlay_merge - Merge an overlay into its base device tree
606  * @fdt: Base Device Tree blob
607  * @fdto: Device tree overlay blob
608  *
609  * overlay_merge() merges an overlay into its base device tree.
610  *
611  * This is the next to last step in the device tree overlay application
612  * process, when all the phandles have been adjusted and resolved and
613  * you just have to merge overlay into the base device tree.
614  *
615  * returns:
616  *      0 on success
617  *      Negative error code on failure
618  */
619 static int overlay_merge(void *fdt, void *fdto)
620 {
621 	int fragment;
622 
623 	fdt_for_each_subnode(fragment, fdto, 0) {
624 		int overlay;
625 		int target;
626 		int ret;
627 
628 		/*
629 		 * Each fragments will have an __overlay__ node. If
630 		 * they don't, it's not supposed to be merged
631 		 */
632 		overlay = fdt_subnode_offset(fdto, fragment, "__overlay__");
633 		if (overlay == -FDT_ERR_NOTFOUND)
634 			continue;
635 
636 		if (overlay < 0)
637 			return overlay;
638 
639 		target = overlay_get_target(fdt, fdto, fragment, NULL);
640 		if (target < 0)
641 			return target;
642 
643 		ret = overlay_apply_node(fdt, target, fdto, overlay);
644 		if (ret)
645 			return ret;
646 	}
647 
648 	return 0;
649 }
650 
651 static int get_path_len(const void *fdt, int nodeoffset)
652 {
653 	int len = 0, namelen;
654 	const char *name;
655 
656 	FDT_RO_PROBE(fdt);
657 
658 	for (;;) {
659 		name = fdt_get_name(fdt, nodeoffset, &namelen);
660 		if (!name)
661 			return namelen;
662 
663 		/* root? we're done */
664 		if (namelen == 0)
665 			break;
666 
667 		nodeoffset = fdt_parent_offset(fdt, nodeoffset);
668 		if (nodeoffset < 0)
669 			return nodeoffset;
670 		len += namelen + 1;
671 	}
672 
673 	/* in case of root pretend it's "/" */
674 	if (len == 0)
675 		len++;
676 	return len;
677 }
678 
679 /**
680  * overlay_symbol_update - Update the symbols of base tree after a merge
681  * @fdt: Base Device Tree blob
682  * @fdto: Device tree overlay blob
683  *
684  * overlay_symbol_update() updates the symbols of the base tree with the
685  * symbols of the applied overlay
686  *
687  * This is the last step in the device tree overlay application
688  * process, allowing the reference of overlay symbols by subsequent
689  * overlay operations.
690  *
691  * returns:
692  *      0 on success
693  *      Negative error code on failure
694  */
695 static int overlay_symbol_update(void *fdt, void *fdto)
696 {
697 	int root_sym, ov_sym, prop, path_len, fragment, target;
698 	int len, frag_name_len, ret, rel_path_len;
699 	const char *s, *e;
700 	const char *path;
701 	const char *name;
702 	const char *frag_name;
703 	const char *rel_path;
704 	const char *target_path;
705 	char *buf;
706 	void *p;
707 
708 	ov_sym = fdt_subnode_offset(fdto, 0, "__symbols__");
709 
710 	/* if no overlay symbols exist no problem */
711 	if (ov_sym < 0)
712 		return 0;
713 
714 	root_sym = fdt_subnode_offset(fdt, 0, "__symbols__");
715 
716 	/* it no root symbols exist we should create them */
717 	if (root_sym == -FDT_ERR_NOTFOUND)
718 		root_sym = fdt_add_subnode(fdt, 0, "__symbols__");
719 
720 	/* any error is fatal now */
721 	if (root_sym < 0)
722 		return root_sym;
723 
724 	/* iterate over each overlay symbol */
725 	fdt_for_each_property_offset(prop, fdto, ov_sym) {
726 		path = fdt_getprop_by_offset(fdto, prop, &name, &path_len);
727 		if (!path)
728 			return path_len;
729 
730 		/* verify it's a string property (terminated by a single \0) */
731 		if (path_len < 1 || memchr(path, '\0', path_len) != &path[path_len - 1])
732 			return -FDT_ERR_BADVALUE;
733 
734 		/* keep end marker to avoid strlen() */
735 		e = path + path_len;
736 
737 		if (*path != '/')
738 			return -FDT_ERR_BADVALUE;
739 
740 		/* get fragment name first */
741 		s = strchr(path + 1, '/');
742 		if (!s) {
743 			/* Symbol refers to something that won't end
744 			 * up in the target tree */
745 			continue;
746 		}
747 
748 		frag_name = path + 1;
749 		frag_name_len = s - path - 1;
750 
751 		/* verify format; safe since "s" lies in \0 terminated prop */
752 		len = sizeof("/__overlay__/") - 1;
753 		if ((e - s) > len && (memcmp(s, "/__overlay__/", len) == 0)) {
754 			/* /<fragment-name>/__overlay__/<relative-subnode-path> */
755 			rel_path = s + len;
756 			rel_path_len = e - rel_path - 1;
757 		} else if ((e - s) == len
758 			   && (memcmp(s, "/__overlay__", len - 1) == 0)) {
759 			/* /<fragment-name>/__overlay__ */
760 			rel_path = "";
761 			rel_path_len = 0;
762 		} else {
763 			/* Symbol refers to something that won't end
764 			 * up in the target tree */
765 			continue;
766 		}
767 
768 		/* find the fragment index in which the symbol lies */
769 		ret = fdt_subnode_offset_namelen(fdto, 0, frag_name,
770 					       frag_name_len);
771 		/* not found? */
772 		if (ret < 0)
773 			return -FDT_ERR_BADOVERLAY;
774 		fragment = ret;
775 
776 		/* an __overlay__ subnode must exist */
777 		ret = fdt_subnode_offset(fdto, fragment, "__overlay__");
778 		if (ret < 0)
779 			return -FDT_ERR_BADOVERLAY;
780 
781 		/* get the target of the fragment */
782 		ret = overlay_get_target(fdt, fdto, fragment, &target_path);
783 		if (ret < 0)
784 			return ret;
785 		target = ret;
786 
787 		/* if we have a target path use */
788 		if (!target_path) {
789 			ret = get_path_len(fdt, target);
790 			if (ret < 0)
791 				return ret;
792 			len = ret;
793 		} else {
794 			len = strlen(target_path);
795 		}
796 
797 		ret = fdt_setprop_placeholder(fdt, root_sym, name,
798 				len + (len > 1) + rel_path_len + 1, &p);
799 		if (ret < 0)
800 			return ret;
801 
802 		if (!target_path) {
803 			/* again in case setprop_placeholder changed it */
804 			ret = overlay_get_target(fdt, fdto, fragment, &target_path);
805 			if (ret < 0)
806 				return ret;
807 			target = ret;
808 		}
809 
810 		buf = p;
811 		if (len > 1) { /* target is not root */
812 			if (!target_path) {
813 				ret = fdt_get_path(fdt, target, buf, len + 1);
814 				if (ret < 0)
815 					return ret;
816 			} else
817 				memcpy(buf, target_path, len + 1);
818 
819 		} else
820 			len--;
821 
822 		buf[len] = '/';
823 		memcpy(buf + len + 1, rel_path, rel_path_len);
824 		buf[len + 1 + rel_path_len] = '\0';
825 	}
826 
827 	return 0;
828 }
829 
830 int fdt_overlay_apply(void *fdt, void *fdto)
831 {
832 	uint32_t delta;
833 	int ret;
834 
835 	FDT_RO_PROBE(fdt);
836 	FDT_RO_PROBE(fdto);
837 
838 	ret = fdt_find_max_phandle(fdt, &delta);
839 	if (ret)
840 		goto err;
841 
842 	ret = overlay_adjust_local_phandles(fdto, delta);
843 	if (ret)
844 		goto err;
845 
846 	ret = overlay_update_local_references(fdto, delta);
847 	if (ret)
848 		goto err;
849 
850 	ret = overlay_fixup_phandles(fdt, fdto);
851 	if (ret)
852 		goto err;
853 
854 	ret = overlay_merge(fdt, fdto);
855 	if (ret)
856 		goto err;
857 
858 	ret = overlay_symbol_update(fdt, fdto);
859 	if (ret)
860 		goto err;
861 
862 	/*
863 	 * The overlay has been damaged, erase its magic.
864 	 */
865 	fdt_set_magic(fdto, ~0);
866 
867 	return 0;
868 
869 err:
870 	/*
871 	 * The overlay might have been damaged, erase its magic.
872 	 */
873 	fdt_set_magic(fdto, ~0);
874 
875 	/*
876 	 * The base device tree might have been damaged, erase its
877 	 * magic.
878 	 */
879 	fdt_set_magic(fdt, ~0);
880 
881 	return ret;
882 }
883