util/kconfig: Add README.md documenting the uprev procedure

Change-Id: I2e74f1c5cb1657e11d4f7ea101549329274102db
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57879
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Singer <felixsinger@posteo.net>

1 files changed, 39 insertions, 0 deletions

diff --git a/util/kconfig/README.md b/util/kconfig/README.md
new file mode 100644
index 000000000000..1350e0430069
--- /dev/null
+++ b/util/kconfig/README.md
@@ -0,0 +1,39 @@
+# coreboot kconfig
+
+This is coreboot's copy of kconfig which tracks Linux as upstream but comes
+with a few patches for portability but also a few semantic changes.
+
+The patches that lead to this tree can be found in the patches/ subdirectory
+in a [quilt](http://savannah.nongnu.org/projects/quilt) friendly format that
+is also simple enough to manage manually with Unix tooling.
+
+## Updating kconfig
+
+The first step is to unapply the patches. This can either be done with quilt
+in an already-configured tree (`quilt pop -a` should cleanly unapply them all)
+or manually if quilt doesn't have its tracking metadata around yet:
+
+    $ for i in `ls patches/*.patch | tac`; do patch -p1 -R -i "$i"; done
+
+The result should be a subtree that, apart from a few coreboot specific
+files on our side (e.g. documentation, integration in our build system)
+and a few files on the upstream end that we don't carry (e.g. the tests),
+is identical to the scripts/kconfig/ directory of Linux as of the most recent
+uprev we did. Check the uprev version by looking through
+`git log util/kconfig` output in our tree.
+
+Assuming that you want to uprev from Linux 5.13 to 5.14, with a Linux git tree
+available in ~/linux,
+
+    $ cd util/kconfig && (cd ~/linux/ && git diff v5.13..v5.14 scripts/kconfig) | patch -p2`
+
+applies the changes to your local tree.
+
+Then reapply our patch train, which might be as simple as
+`quilt push -a --refresh` but might also require some meddling with the
+patches to make them apply again with the changes you just imported from
+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.