Re: [PATCH v4 01/10] of: Add test managed wrappers for of_overlay_apply()/of_node_put()

[Rob Herring <robh@kernel.org>]

On Mon, 22 Apr 2024 16:23:54 -0700, Stephen Boyd wrote:
> 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:
> 
>  1) 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.
> 
>  2) 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.
> 
>  3) 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.
> 
>  4) 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>
> Signed-off-by: Stephen Boyd <sboyd@kernel.org>
> ---
>  Documentation/dev-tools/kunit/api/index.rst | 11 +++
>  Documentation/dev-tools/kunit/api/of.rst    | 13 +++
>  drivers/of/Makefile                         |  1 +
>  drivers/of/of_kunit.c                       | 99 +++++++++++++++++++++
>  include/kunit/of.h                          | 94 +++++++++++++++++++
>  5 files changed, 218 insertions(+)
>  create mode 100644 Documentation/dev-tools/kunit/api/of.rst
>  create mode 100644 drivers/of/of_kunit.c
>  create mode 100644 include/kunit/of.h
> 

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>