linux-kernel - Re: [RFC PATCH 1/1] drm/format-helper: Add KUnit tests for drm_fb_xrgb8888_to

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Date:   Mon, 30 May 2022 15:57:56 -0700
From:   Daniel Latypov <dlatypov@...gle.com>
To:     José Expósito <jose.exposito89@...il.com>
Cc:     Maxime Ripard <maxime@...no.tech>, kunit-dev@...glegroups.com,
        javierm@...hat.com, tzimmermann@...e.de,
        maarten.lankhorst@...ux.intel.com, airlied@...ux.ie,
        daniel@...ll.ch, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] drm/format-helper: Add KUnit tests for drm_fb_xrgb8888_to_rgb332()

On Mon, May 30, 2022 at 9:29 AM José Expósito <jose.exposito89@...il.com> wrote:
> I just cc'ed kunit-dev@...glegroups.com. For anyone joining the
> conversation, here is the link to the patch and the cover letter with
> some questions:
>
> https://lore.kernel.org/dri-devel/20220530102017.471865-1-jose.exposito89@gmail.com/T/

Thanks for the link.
A few initial notes:
a) normally, `select`ing other kconfigs is discouraged. It's not
explicitly called out in
https://www.kernel.org/doc/html/latest/dev-tools/kunit/style.html#test-kconfig-entries
but this was the conclusion after  some debate on the mailing lists
earlier.
b) I see `dst` is allocated with kzalloc but not freed. Should we use
`kunit_kzalloc()` instead so it does get automatically freed?

>
> >
> > > ---
> > >  drivers/gpu/drm/Kconfig                  |  12 ++
> > >  drivers/gpu/drm/Makefile                 |   3 +
> > >  drivers/gpu/drm/drm_format_helper_test.c | 166 +++++++++++++++++++++++
> > >  3 files changed, 181 insertions(+)
> > >  create mode 100644 drivers/gpu/drm/drm_format_helper_test.c
> > >
> > > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> > > index e88c497fa010..d92be6faef15 100644
> > > --- a/drivers/gpu/drm/Kconfig
> > > +++ b/drivers/gpu/drm/Kconfig
> > > @@ -76,6 +76,18 @@ config DRM_KMS_HELPER
> > >     help
> > >       CRTC helpers for KMS drivers.
> > >
> > > +config DRM_FORMAR_HELPER_TEST
> > > +   bool "drm_format_helper tests" if !KUNIT_ALL_TESTS
> > > +   depends on DRM && KUNIT=y
> > > +   select DRM_KMS_HELPER

>From above, a)
Specifically here, it'd be encouraged to instead do
  depends on DRM && KUNIT=y && DRM_KMS_HELPER

Ideally, using a .kunitconfig file would make it so having to select
DRM_KMS_HELPER manually isn't that annoying.

> > AFAIK, kunit test cases are supposed to have a .kunitconfig too to
> > enable the kunit tests easily.
> >
> > Maxime
>
> A .kuniconfig example is present in the cover letter. My understanding
> from the docs:
>
> https://docs.kernel.org/dev-tools/kunit/run_wrapper.html#create-a-kunitconfig-file

The bit of the documentation you're looking for is
https://www.kernel.org/doc/html/latest/dev-tools/kunit/running_tips.html#defining-a-set-of-tests
You can create a drivers/gpu/drm/.kunitconfig file and run with
$ ./tools/testing/kunit/kunit.py run --kunitconfig=drivers/gpu/drm --arch=x86_86

The contents of that file would be just like
  CONFIG_KUNIT=y
  CONFIG_DRM=y
  CONFIG_DRM_KMS_HELPER=y  # if no `select`
  CONFIG_DRM_FORMAR_HELPER_TEST=y

Re "kunit test cases are supposed to have a .kunitconfig too"
As I noted in the docs:
  This is a relatively new feature (5.12+) so we don’t have any
conventions yet about on what files should be checked in versus just
kept around locally. It’s up to you and your maintainer to decide if a
config is useful enough to submit (and therefore have to maintain).

So it's up to whatever people think works best/is worth it.
I think in this case, it makes sense to add the file.

> Is that, like the .config file, the .kunitconfig file is not meant to
> be included in git, but I'm sure someone else will clarify this point.

That bit of the docs needs to be rewritten.
You're recommended to check in a drivers/gpu/drm/.kunitconfig file into git.

Context: `kunit.py` used to use the "<root>/.kunitconfig" file.
Anytime you wanted to run more tests, you'd append to that file.
So we agreed that no one should check in that file specifically.

Now kunit.py
* uses "<build-dir>/.kunitconfig", by default: ".kunit/.kunitconfig"
* has the --kunitconfig flag so you can use different files
so it's no longer as relevant.

Hope that helps,
Daniel