linux-kernel - Re: [PATCH 0/4] KUnit tests for RGB565 conversion

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Message-ID: <20220703151926.GA130430@elementary>
Date:   Sun, 3 Jul 2022 17:19:26 +0200
From:   José Expósito <jose.exposito89@...il.com>
To:     David Gow <davidgow@...gle.com>
Cc:     Javier Martinez Canillas <javierm@...hat.com>,
        Daniel Latypov <dlatypov@...gle.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Maxime Ripard <mripard@...nel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        maarten.lankhorst@...ux.intel.com,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Maíra Canal <maira.canal@....br>,
        Isabella Basso <isabbasso@...eup.net>, magalilemes00@...il.com,
        tales.aparecida@...il.com, dri-devel@...ts.freedesktop.org,
        KUnit Development <kunit-dev@...glegroups.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] KUnit tests for RGB565 conversion

Hi David,

Sorry for not getting back to you sooner, I've been swamped with work
this week.

On Wed, Jun 29, 2022 at 03:27:44PM +0800, David Gow wrote:
> These look pretty good overall to me, but there is one big issue
> (which is actually with the previous series -- oops!), and a few small
> stylistic thoughts.
> 
> For the big issue: these tests don't work on big-endian systems. The
> 'swab' bit in this series reminded me to check, and sure enough, all
> of the tests fail (including the rgb332 ones).
> 
> I tested it on PowerPC with:
>  ./tools/testing/kunit/kunit.py run
> --kunitconfig=drivers/gpu/drm/tests --arch=powerpc
> --cross_compile=powerpc64-linux-gnu-
> 
> So that's something which needs to be fixed.

Oops, yes, definitely something that I need to fix!
I'll include an extra patch at the beginning of v2 fixing this bug.

> The smaller stylistic thoughts basically all revolve around the
> complexity of convert_xrgb8888_cases: there are arrays of structs with
> arrays of unions of structs (with function pointers in them). This
> isn't a problem: it's actually a lot more readable than that
> description implies, but there are other ways it could be tackled
> (which have their own tradeoffs, of course).
> 
> One possibility would be to split up the test into a separate test per
> destination format. They could reuse the convert_xrgb8888_cases array,
> and just each access a different result. You could make things even
> clearer (IMO) by replacing the results[] array with a separate, named,
> member (since you don't need to iterate over them any more), and
> remove the need to have the function pointer and swab union/members by
> just hardcoding those in the separate test functions. It'd also make
> the results a bit clearer, as each destination format would get its
> own separate set of results.
> 
> Of course, that's just an idea: I don't actually have a problem with
> the existing design either (other than the endianness issue, of
> course).

I like from your approach that the output of the tests would be easier
to understand. At the moment, if a test fails, there is not enough
context to know which target format failed. I'll explore this approach
and see how it looks like.

Thanks,
Jose

> Cheers,
> -- David