linux-kernel - Re: [PATCH v4 1/6] drm/format-helper: Add drm_fb_xrgb8888_to_gray8

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Date:   Fri, 11 Feb 2022 13:11:25 +0100
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-fbdev@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Noralf Trønnes <noralf@...nnes.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Maxime Ripard <maxime@...no.tech>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH v4 1/6] drm/format-helper: Add
 drm_fb_xrgb8888_to_gray8_line()

Hello Jani,

On 2/11/22 13:05, Jani Nikula wrote:

[snip]

>>>> I don't see why a while loop would be an improvement here TBH.
>>>
>>> Less letters to parse when reading the code.
>>
>> It's a simple refactoring of code that has worked well so far. Let's 
>> leave it as-is for now.
> 
> IMO *always* prefer a for loop over while or do-while.
> 
> The for (i = 0; i < N; i++) is such a strong paradigm in C. You
> instantly know how many times you're going to loop, at a glance. Not so
> with with the alternatives, which should be used sparingly.
> 
> And yes, the do-while suggested above is buggy, and you actually need to
> stop and think to see why.
>

Absolutely agree.

These format conversion helpers are not trivial to read and understand (at
least for me). In my opinion the code should be written in a way that ease
readability and make as robust and less error prone as possible.
 
> 
> BR,
> Jani.
Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat