tjh.dev
1from argparse import ArgumentParser
2from dataclasses import dataclass
3from functools import cached_property
4import json
5from pathlib import Path
6import shutil
7
8from libfdt import Fdt, FdtException, FDT_ERR_NOSPACE, FDT_ERR_NOTFOUND, fdt_overlay_apply
9
10
11@dataclass
12class Overlay:
13 name: str
14 filter: str
15 dtbo_file: Path
16
17 @cached_property
18 def fdt(self) -> Fdt:
19 with self.dtbo_file.open("rb") as fd:
20 return Fdt(fd.read())
21
22 @cached_property
23 def compatible(self) -> set[str]:
24 return get_compatible(self.fdt)
25
26
27def get_compatible(fdt) -> set[str]:
28 root_offset = fdt.path_offset("/")
29
30 try:
31 return set(fdt.getprop(root_offset, "compatible").as_stringlist())
32 except FdtException as e:
33 if e.err == -FDT_ERR_NOTFOUND:
34 return set()
35 else:
36 raise e
37
38
39def apply_overlay(dt: Fdt, dto: Fdt) -> Fdt:
40 while True:
41 # we need to copy the buffers because they can be left in an inconsistent state
42 # if the operation fails (ref: fdtoverlay source)
43 result = dt.as_bytearray().copy()
44 err = fdt_overlay_apply(result, dto.as_bytearray().copy())
45
46 if err == 0:
47 new_dt = Fdt(result)
48 # trim the extra space from the final tree
49 new_dt.pack()
50 return new_dt
51
52 if err == -FDT_ERR_NOSPACE:
53 # not enough space, add some blank space and try again
54 # magic number of more space taken from fdtoverlay
55 dt.resize(dt.totalsize() + 65536)
56 continue
57
58 raise FdtException(err)
59
60def process_dtb(rel_path: Path, source: Path, destination: Path, overlays_data: list[Overlay]):
61 source_dt = source / rel_path
62 print(f"Processing source device tree {rel_path}...")
63 with source_dt.open("rb") as fd:
64 dt = Fdt(fd.read())
65
66 for overlay in overlays_data:
67 if overlay.filter and overlay.filter not in str(rel_path):
68 print(f" Skipping overlay {overlay.name}: filter does not match")
69 continue
70
71 dt_compatible = get_compatible(dt)
72 if len(dt_compatible) == 0:
73 print(f" Device tree {rel_path} has no compatible string set. Assuming it's compatible with overlay")
74 elif not overlay.compatible.intersection(dt_compatible):
75 print(f" Skipping overlay {overlay.name}: {overlay.compatible} is incompatible with {dt_compatible}")
76 continue
77
78 print(f" Applying overlay {overlay.name}")
79 dt = apply_overlay(dt, overlay.fdt)
80
81 print(f"Saving final device tree {rel_path}...")
82 dest_path = destination / rel_path
83 dest_path.parent.mkdir(parents=True, exist_ok=True)
84 with dest_path.open("wb") as fd:
85 fd.write(dt.as_bytearray())
86
87def main():
88 parser = ArgumentParser(description='Apply a list of overlays to a directory of device trees')
89 parser.add_argument("--source", type=Path, help="Source directory")
90 parser.add_argument("--destination", type=Path, help="Destination directory")
91 parser.add_argument("--overlays", type=Path, help="JSON file with overlay descriptions")
92 args = parser.parse_args()
93
94 source: Path = args.source
95 destination: Path = args.destination
96 overlays: Path = args.overlays
97
98 with overlays.open() as fd:
99 overlays_data = [
100 Overlay(
101 name=item["name"],
102 filter=item["filter"],
103 dtbo_file=Path(item["dtboFile"]),
104 )
105 for item in json.load(fd)
106 ]
107
108 for dirpath, dirnames, filenames in source.walk():
109 for filename in filenames:
110 rel_path = (dirpath / filename).relative_to(source)
111 if filename.endswith(".dtb"):
112 process_dtb(rel_path, source, destination, overlays_data)
113 else:
114 # Copy other files through
115 dest_path = destination / rel_path
116 dest_path.parent.mkdir(parents=True, exist_ok=True)
117 shutil.copy(source / rel_path, dest_path)
118
119
120if __name__ == '__main__':
121 main()