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

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Date:   Thu, 2 Apr 2020 11:52:16 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>
Cc:     Petr Mladek <pmladek@...e.com>, mchehab@...nel.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        hverkuil@...all.nl,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        laurent.pinchart@...asonboard.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-media@...r.kernel.org,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>
Subject: Re: [PATCH 1/1] lib/vsprintf: Add support for printing V4L2 and DRM
 fourccs

Moi,

On Thu, Apr 02, 2020 at 11:34:48AM +0300, Jani Nikula wrote:
> On Wed, 01 Apr 2020, Sakari Ailus <sakari.ailus@...ux.intel.com> 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.
> 
> I'm not going to take a strong stand in one way or the other regarding
> the patch at hand, but I do think at some point we have to draw a line
> what should be included in printk formats. Arguably they should be
> reserved to things that are generally useful across large parts of the
> kernel, right?
> 
> I think the more specialized you get, the more you should think about
> just using the plain old %s, and your own helpers. Because frankly, the
> kernel printk specifiers also start getting more than a little obscure.

I don't really disagree... While this is functionality very commonly needed
in drivers, there are alternatives such as posted here:

<URL:https://lore.kernel.org/linux-media/20190916100433.24367-1-hverkuil-cisco@xs4all.nl/>

The 4cc codes added by this set is still relatively generic (while still
Linux subsystem specific and not related to e.g. hardware standards), but I
wonder how many other, possibly similar cases there could be in the kernel,
and how many new specifiers we might get with those all added.

For what it's worth, even C99 defines macros for printing some formats
such as PRIu64 for uint64_t.

-- 
Terveisin,

Sakari Ailus