linux-kernel - Re: [PATCH v6 2/3] v4l: ioctl: Use %p4cc printk modifier to print FourCC codes

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Message-ID: <YCVb8hxawwd2l2yx@alley>
Date:   Thu, 11 Feb 2021 17:31:46 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        dri-devel@...ts.freedesktop.org, hverkuil@...all.nl,
        laurent.pinchart@...asonboard.com, mchehab@...nel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joe Perches <joe@...ches.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v6 2/3] v4l: ioctl: Use %p4cc printk modifier to print
 FourCC codes

On Mon 2021-02-08 22:09:02, Sakari Ailus wrote:
> Now that we can print FourCC codes directly using printk, make use of the
> feature in V4L2 core.
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> ---
>  drivers/media/v4l2-core/v4l2-ioctl.c | 85 +++++++---------------------
>  1 file changed, 21 insertions(+), 64 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 31d1342e61e8..31662c3a8c9e 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -265,13 +265,9 @@ static void v4l_print_fmtdesc(const void *arg, bool write_only)
>  {
>  	const struct v4l2_fmtdesc *p = arg;
>  
> -	pr_cont("index=%u, type=%s, flags=0x%x, pixelformat=%c%c%c%c, mbus_code=0x%04x, description='%.*s'\n",
> +	pr_cont("index=%u, type=%s, flags=0x%x, pixelformat=%p4cc, mbus_code=0x%04x, description='%.*s'\n",

Is %p4cc really acceptable here?

The original code printed only the 4 characters. The original code
would print something like:

  index=21, type=bla, flags=0x0, pixelformat=BG12, mbus_code=0x0a9f, descrition="bla bla bla"

while the new code will do:

  index=21, type=bla, flags=0x0, pixelformat=BG12 little-endian (0x32314742), mbus_code=0x0a9f, descrition="bla bla bla"

This is much harder to parse because there are spaces also inside pixel_format=<value>



>  		p->index, prt_names(p->type, v4l2_type_names),
> -		p->flags, (p->pixelformat & 0xff),
> -		(p->pixelformat >>  8) & 0xff,
> -		(p->pixelformat >> 16) & 0xff,
> -		(p->pixelformat >> 24) & 0xff,
> -		p->mbus_code,
> +		p->flags, &p->pixelformat, p->mbus_code,
>  		(int)sizeof(p->description), p->description);
>  }
>  

Best Regards,
Petr