linux-kernel - Re: [PATCH v2 1/1] lib/vsprintf: Add support for printing V4L2 and DRM fourccs

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Date:   Fri, 03 Apr 2020 09:56:42 -0700
From:   Joe Perches <joe@...ches.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Petr Mladek <pmladek@...e.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-media@...r.kernel.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        hverkuil@...all.nl, laurent.pinchart@...asonboard.com,
        mchehab@...nel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>
Subject: Re: [PATCH v2 1/1] lib/vsprintf: Add support for printing V4L2 and
 DRM fourccs

On Fri, 2020-04-03 at 14:10 +0200, Rasmus Villemoes wrote:
> On 03/04/2020 11.11, Sakari Ailus wrote:
> > Add a printk modifier %ppf (for pixel format) for printing V4L2 and DRM
> > pixel formats denoted by 4ccs. The 4cc encoding is the same for both so
> > the same implementation can be used.
> 
> This seems quite niche to me, I'm not sure that belongs in vsprintf.c.
> What's wrong with having a
> 
> char *fourcc_string(char *buf, u32 x)
> 
> that formats x into buf and returns buf, so it can be used in a
> 
> char buf[8];
> pr_debug("bla: %s\n", fourcc_string(buf, x))

Nothing really, it's a number of uses question.

For networking code,  print_mac was used before %pM.

After Linus floated the idea of %p<foo>, %pM was
introduced and all the DECLARE_MAC_BUF/print_mac
calls were converted.

%pM did reduce overall object size a fair amount.

How many instances of %p4cc could there be?