There are two ways to submit changes for dtc or libfdt:
The shared library uses libfdt/version.lds to list the exported functions, so add your new function there. Check that your function works with pylibfdt. If it cannot be supported, put the declaration in libfdt.h behind #ifndef SWIG so that swig ignores it.
Test files are kept in the tests/ directory. Use make check to build and run all tests.
If you want to adjust a test file, be aware that tree_tree1.dts is compiled and checked against a binary tree from assembler macros in trees.S. So if you change that file you must change tree.S also.
Like many other projects, dtc and libfdt have adopted the "Developer's Certificate of Origin" (Signed-off-by) process created by the Linux kernel community to improve tracking of who did what. Here's how it works (this is a very slight modification of the description from Documentation/process/submitting-patches.rst in the kernel tree):
The sign-off is a simple line at the end of the explanation for the patch, which certifies that you wrote it or otherwise have the right to pass it on as an open-source patch. The rules are pretty simple: if you can certify the below:
Developer's Certificate of Origin 1.1
By making a contribution to this project, I certify that:
(a) The contribution was created in whole or in part by me and I
have the right to submit it under the open source license
indicated in the file; or
(b) The contribution is based upon previous work that, to the best
of my knowledge, is covered under an appropriate open source
license and I have the right under that license to submit that
work with modifications, whether created in whole or in part
by me, under the same open source license (unless I am
permitted to submit under a different license), as indicated
in the file; or
(c) The contribution was provided directly to me by some other
person who certified (a), (b) or (c) and I have not modified
it.
(d) I understand and agree that this project and the contribution
are public and that a record of the contribution (including all
personal information I submit with it, including my sign-off) is
maintained indefinitely and may be redistributed consistent with
this project or the open source license(s) involved.
then you just add a line saying::
Signed-off-by: Random J Developer <random@developer.example.org>
using your real name (sorry, no pseudonyms or anonymous contributions.) This will be done for you automatically if you use git commit -s. Reverts should also include "Signed-off-by". git revert -s does that for you.
Any further SoBs (Signed-off-by:'s) following the author's SoB are from people handling and transporting the patch, but were not involved in its development. SoB chains should reflect the real route a patch took as it was propagated to the maintainers, with the first SoB entry signalling primary authorship of a single author.