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

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Date:   Fri, 3 Apr 2020 19:32:42 +0200
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Petr Mladek <pmladek@...e.com>,
        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,
        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

Em Fri, 03 Apr 2020 09:56:42 -0700
Joe Perches <joe@...ches.com> escreveu:

> 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?

That's hard to know... there are several places printing it
with different ways:

	$ git grep -i -E "(dev|pr)_(warn|dbg|info)" drivers/media|grep pixf|wc -l
	6
	$ git grep -i -E "print" drivers/media|grep pixf|wc -l
	1
	$ git grep print_fourcc|wc -l
	7
	$ git grep -i -E "(dev|pr)_(warn|dbg|info)" drivers/media|grep pixelf|wc -l
	10
	$ git grep -i -E "(dev|pr|v4l)_(warn|dbg|info)" drivers/media|grep format|wc -l
	60

I bet there are other places besides the above ones, but the thing is, as 
we currently lack a standard way, drivers still have their own ideas
about how to handle it. Each one does it differently.


Thanks,
Mauro