util/kconfig/README.md: Add notes about adding a new quilt patch

The patches for kconfig need to be in a format compatible with the quilt
tool, and usually also contain a header with some additional info like
the git commit. This header is in the same format as patches produced by
`git format-patch`, but the diff style git uses is incompatible with
quilt and there does not seem to be a straightforward way to format the
diff section to work.

Add some documentation for a method I found to go from a git commit to a
quilt compatible patch with git headers.

Change-Id: I7a8bbe41e0864be1d28116742b6b8b3fc440cc31
Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69458
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/util/kconfig/README.md b/util/kconfig/README.md
index 1350e04300..4d508a5e19 100644
--- a/util/kconfig/README.md
+++ b/util/kconfig/README.md
@@ -37,3 +37,44 @@ Linux.
 Check that kconfig still works, `git add` and `git commit` the changes and
 write a meaningful commit message that documents what Linux kconfig version
 the tree has been upreved to.
+
+## Adding a new patch
+The format of the patches to kconfig is a mix of the headers produced by `git
+format-patch` and the patch format of quilt. However neither git nor quilt
+seems to have any functionality to directly produce a file in such a format
+
+To add a patch in this format:
+1. Add your changes to the sources and `git commit` them
+2. Generate a git patch for the commit:
+
+    $ git format-patch HEAD~
+
+3. Reverse apply the newly created patch file to restore the tree back to the
+   state quilt thinks it is in:
+
+    $ git apply -R <the patch file>
+
+4. Import the patch info quilt:
+
+    $ quilt import <the patch file>
+
+5. Force push the change to the top of quilt's patch stack (quilt won't like
+   the git diff style and would normally refuse to apply the patch):
+
+    $ quilt push -f <the patch file>
+
+6. Add the changed files to be tracked against the quilt:
+
+    $ quilt add <the files you changed>
+
+7. Re-apply your changes from the patch file:
+
+    $ git apply <the patch file>
+
+8. Add the changes to quilt to regenerate the patch file in a quilt compatible
+   format while keeping the git header:
+
+    $ quilt refresh
+
+9. The new patch file and updated patches/series files can now be added to the
+   git commit