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

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Date:   Mon, 06 Apr 2020 06:01:17 -0700
From:   Joe Perches <joe@...ches.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
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 Mailing List <linux-media@...r.kernel.org>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Laurent Pinchart <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

On Mon, 2020-04-06 at 13:44 +0300, Andy Shevchenko wrote:
> On Mon, Apr 6, 2020 at 10:46 AM Mauro Carvalho Chehab
> <mchehab+huawei@...nel.org> wrote:
> > Em Fri, 3 Apr 2020 21:32:42 +0300
> > Andy Shevchenko <andy.shevchenko@...il.com> escreveu:
> > > On Fri, Apr 3, 2020 at 8:54 PM Joe Perches <joe@...ches.com> wrote:
> > > > On Fri, 2020-04-03 at 19:32 +0200, Mauro Carvalho Chehab wrote:
> > > > > Em Fri, 03 Apr 2020 09:56:42 -0700
> > > > > Joe Perches <joe@...ches.com> escreveu:
> > > > It _might_ be useful to use a CONFIG_MEDIA_SUPPORT guard
> > > > in lib/vsprintf for this.
> > > 
> > > No need. FourCC, if Sakari makes it more generic, can be used for
> > > other purposes, e.g. printing component names from the chips (not
> > > related to media at all).
> > > 
> > 
> > Hmm... not 100% sure about what you're meaning with "component names".
> 
> 4cc is pretty much wide standard, media is just one of (famous) users of it.
> 
> As I emphasized the example I referring to has nothing to do with media.
> 
> Now, I have already two examples:
> - component name inside hardware register (used by Synopsys DesignWare)
> - CSRT table in ACPI uses this code for vendor ID.

So if this is really u32_to_ascii, perhaps the "-BE" bit
should be separated and "%4pEp" could be used with some
renamed inline used like ERR_PTR so maybe something like
this might work?

static inline void * __must_check FOURCC(u32 val)
{
	return (void *)(unsigned long)cpu_to_be32(val);
}

void test_4cc(void)
{
	u32 val = 0x41424344;

	printk("4cc like: %4pE\n", FOURCC(val));
}