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

[Mauro Carvalho Chehab]

Em Fri, 03 Apr 2020 09:56:42 -0700
Joe Perches <joe@xxxxxxxxxxx> 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