Quoting Stephen Boyd (2024-07-18 14:05:01)
Add test managed wrappers for of_overlay_apply() that automatically removes the overlay when the test is finished. This API is intended for use by KUnit tests that test code which relies on 'struct device_node's and of_*() APIs.
KUnit tests will call of_overlay_apply_kunit() to load an overlay that's been built into the kernel image. When the test is complete, the overlay will be removed.
This has a few benefits:
It keeps the tests hermetic because the overlay is removed when the test is complete. Tests won't even be aware that an overlay was loaded in another test.
The overlay code can live right next to the unit test that loads it. The overlay and the unit test can be compiled into one kernel module if desired.
We can test different device tree configurations by loading different overlays. The overlays can be written for a specific test, and there can be many of them loaded per-test without needing to jam all possible combinations into one DTB.
It also allows KUnit to test device tree dependent code on any architecture, not just UML. This allows KUnit tests to test architecture specific device tree code.
There are some potential pitfalls though. Test authors need to be careful to not overwrite properties in the live tree. The easiest way to do this is to add and remove nodes with a 'kunit-' prefix, almost guaranteeing that the same node won't be present in the tree loaded at boot.
Suggested-by: Rob Herring robh@kernel.org Cc: Rob Herring robh@kernel.org Cc: Saravana Kannan saravanak@google.com Reviewed-by: Rob Herring (Arm) robh@kernel.org Reviewed-by: David Gow davidgow@google.com Signed-off-by: Stephen Boyd sboyd@kernel.org
Applied to clk-next