linux-kernel - Re: [PATCH v2 13/33] drm/client: Add some tests for drm_connector_pick_cmdline

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Date:   Fri, 23 Sep 2022 11:26:34 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        Maxime Ripard <maxime@...no.tech>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Maxime Ripard <mripard@...nel.org>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Emma Anholt <emma@...olt.net>,
        Karol Herbst <kherbst@...hat.com>,
        Samuel Holland <samuel@...lland.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Daniel Vetter <daniel@...ll.ch>, Lyude Paul <lyude@...hat.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Chen-Yu Tsai <wens@...e.org>
Cc:     Dom Cobley <dom@...pberrypi.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Phil Elwell <phil@...pberrypi.com>,
        nouveau@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Mateusz Kwiatkowski <kfyatek+publicgit@...il.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Noralf Trønnes <noralf@...nnes.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-sunxi@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 13/33] drm/client: Add some tests for
 drm_connector_pick_cmdline_mode()

On 9/23/22 11:15, Thomas Zimmermann wrote:
> Hi
> 
> Am 22.09.22 um 16:25 schrieb Maxime Ripard:
>> drm_connector_pick_cmdline_mode() is in charge of finding a proper
>> drm_display_mode from the definition we got in the video= command line
>> argument.
>>
>> Let's add some unit tests to make sure we're not getting any regressions
>> there.
>>
>> Signed-off-by: Maxime Ripard <maxime@...no.tech>
>>
>> diff --git a/drivers/gpu/drm/drm_client_modeset.c b/drivers/gpu/drm/drm_client_modeset.c
>> index bbc535cc50dd..d553e793e673 100644
>> --- a/drivers/gpu/drm/drm_client_modeset.c
>> +++ b/drivers/gpu/drm/drm_client_modeset.c
>> @@ -1237,3 +1237,7 @@ int drm_client_modeset_dpms(struct drm_client_dev *client, int mode)
>>   	return ret;
>>   }
>>   EXPORT_SYMBOL(drm_client_modeset_dpms);
>> +
>> +#ifdef CONFIG_DRM_KUNIT_TEST
>> +#include "tests/drm_client_modeset_test.c"
>> +#endif
> 
> I strongly dislike this style of including source files in each other. 
> It's a recipe for all kind of build errors. Can you do something else?
>

This seems to be the convention used to test static functions and what's
documented in the Kunit docs: https://kunit.dev/third_party/kernel/docs/tips.html#testing-static-functions

I agree with you that's not ideal but I think that consistency with how
it is done by other subsystems is also important.
 
> As the tested function is an internal interface, maybe export a wrapper 
> if tests are enabled, like this:
> 
> #ifdef CONFIG_DRM_KUNIT_TEST
> struct drm_display_mode *
> drm_connector_pick_cmdline_mode_kunit(drm_conenctor)
> {
>    return drm_connector_pick_cmdline_mode(connector)
> }
> EXPORT_SYMBOL(drm_connector_pick_cmdline_mode_kunit)
> #endif
> 
> The wrapper's declaration can be located in the kunit test file.
> 

But that's also not nice since we are artificially exposing these only
to allow the static functions to be called from unit tests. And would
be a different approach than the one used by all other subsystems...

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat