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

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Date:   Thu, 2 Jun 2022 10:07:56 -0700
From:   David Gow <davidgow@...gle.com>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     José Expósito <jose.exposito89@...il.com>,
        tzimmermann@...e.de, maarten.lankhorst@...ux.intel.com,
        mripard@...nel.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Daniel Latypov <dlatypov@...gle.com>,
        KUnit Development <kunit-dev@...glegroups.com>
Subject: Re: [RFC PATCH 1/1] drm/format-helper: Add KUnit tests for drm_fb_xrgb8888_to_rgb332()

On Thu, Jun 2, 2022 at 9:27 AM Javier Martinez Canillas
<javierm@...hat.com> wrote:
>
> Hello José,
>
> On 5/30/22 12:20, José Expósito wrote:
> > Test the conversion from XRGB8888 to RGB332.
> >
> > What is tested?
> >
> >  - Different values for the X in XRGB8888 to make sure it is ignored
> >  - Different clip values: Single pixel and full and partial buffer
> >  - Well know colors: White, black, red, green, blue, magenta, yellow
> >    and cyan
> >  - Other colors: Randomly picked
> >  - Destination pitch
> >
> > Suggested-by: Javier Martinez Canillas <javierm@...hat.com>
> > Signed-off-by: José Expósito <jose.exposito89@...il.com>
> > ---
>
> Thanks a lot for working on this! It's very cool to see the first KUnit
> tests added to DRM :)
>
> >  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
>
> I wonder if we want this level of detail for the test Kconfig symbols.
> Maybe we could just have a DRM_KUNIT_TEST symbol that will enable all
> the KUnit test suites for DRM ?
>
> > +     bool "drm_format_helper tests" if !KUNIT_ALL_TESTS
> > +     depends on DRM && KUNIT=y
> > +     select DRM_KMS_HELPER
>
> Daniel didn't like this `select DRM_KMS_HELPER` and I think that we can avoid
> it if instead drm_format_helper_test.c is included in drm_format_helper.c, i.e:
>
> diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
> index a3ccd8bc966f..d63e02da528f 100644
> --- a/drivers/gpu/drm/drm_format_helper.c
> +++ b/drivers/gpu/drm/drm_format_helper.c
> @@ -692,3 +692,7 @@ void drm_fb_xrgb8888_to_mono(void *dst, unsigned int dst_pitch, const void *vadd
>         kfree(src32);
>  }
>  EXPORT_SYMBOL(drm_fb_xrgb8888_to_mono);
> +
> +#ifdef DRM_KUNIT_TEST
> +#include "drm_format_helper_test.c"
> +#endif
>
> This also has the advantage that will allow to have KUnit tests for the static
> functions that are only available in the drm_format_helper.c compilation unit.
>
> >  obj-$(CONFIG_DRM_DEBUG_SELFTEST) += selftests/
> > +obj-$(CONFIG_DRM_FORMAR_HELPER_TEST) += drm_kms_helper.o \
> > +             drm_format_helper_test.o
>
> And doing that will also allow you to get rid of this, since just selecting
> CONFIG_DRM_KUNIT_TEST=y would be enough for the tests built and run by KUnit.
>

This is definitely something other KUnit tests (apparmor, elf, etc)
are doing, and it's generally fine. You do lose the ability to build
the tests as a separate module, though. (This is not usually a big
problem, but there are some cases where it's useful.)

That being said, I don't think 'select' is enough of a problem that
you should feel the need to refactor in this way just to avoid it.
Given most of the other DRM drivers (as well as DRM_DEBUG_SELFTEST)
are select-ing DRM_KMS_HELPER, it seems like a sensible enough thing
to continue doing for the KUnit test. As Daniel pointed out, as a
hidden option it was clearly always meant to be select-ed anyway.

Cheers,
-- David