linux-kernel - Re: [PATCH v2 6/6] lib/vsprintf: Add %pfw conversion specifier for printing fwnode names

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Message-ID: <20190329131053.ulncujrh3dwhh6bt@kekkonen.localdomain>
Date:   Fri, 29 Mar 2019 15:10:54 +0200
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org, rafael@...nel.org,
        linux-acpi@...r.kernel.org, devicetree@...r.kernel.org,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v2 6/6] lib/vsprintf: Add %pfw conversion specifier for
 printing fwnode names

Hi Petr,

On Thu, Mar 28, 2019 at 03:29:27PM +0100, Petr Mladek wrote:
> On Tue 2019-03-26 15:24:50, Andy Shevchenko wrote:
> > On Tue, Mar 26, 2019 at 02:11:35PM +0100, Rasmus Villemoes wrote:
> > > On 26/03/2019 13.41, Sakari Ailus wrote:
> > > > Add support for %pfw conversion specifier (with "f" and "P" modifiers) to
> > > > support printing full path of the node, including its name ("f") and only
> > > > the node's name ("P") in the printk family of functions. The two flags
> > > > have equivalent functionality to existing %pOF with the same two modifiers
> > > > ("f" and "P") on OF based systems. The ability to do the same on ACPI
> > > > based systems is added by this patch.
> > 
> > > > +	for (pass = false; strspn(fmt, modifiers); fmt++, pass = true) {
> > > > +		if (pass) {
> > > > +			if (buf < end)
> > > > +				*buf = ':';
> > > > +			buf++;
> > > > +		}
> > > > +
> > > > +		switch (*fmt) {
> > > > +		case 'f':	/* full_name */
> > > > +			buf = fwnode_gen_full_name(fwnode, buf, end);
> > > > +			break;
> > > > +		case 'P':	/* name */
> > > > +			buf = string(buf, end, fwnode_get_name(fwnode),
> > > > +				     str_spec);
> > > > +			break;
> > > > +		default:
> > > > +			break;
> > > > +		}
> > > > +	}
> > > 
> > > This seems awfully complicated. Why would anyone ever pass more than one
> > > of 'f' and 'P'? Why not just
> > > 
> > > switch(*fmt) {
> > > case 'P':
> > >    ...
> > > case 'f':
> > > default:
> > >    ...
> > > }
> > > 
> > > which avoids the loop and the strcspn. Or, drop the default: case and
> > > don't have logic at all for falling back to 'f' if neither is present.
> > > 
> > > > +	return widen_string(buf, buf - buf_start, end, spec);
> > > > +}
> > 
> > My point as well (as per sent comments against previous version).
> > Sakari, can you add test cases at the same time?
> > 
> > > >  			return device_node_string(buf, end, ptr, spec, fmt + 1);
> > 
> > > > +			return fwnode_string(buf, end, ptr, spec, fmt + 1);
> > > 
> > > Why not pass fmt+2; we know that fmt+1 points at a 'w'. Just to avoid
> > > doing the fmt++ inside fwnode_string().
> > 
> > I guess in order to be consistent with existing %pOF case. But wouldn't be
> > better to fix %pOF for that sooner or later?
> 
> Good question. Are there any %pOF users that would want to use the for
> cycle and printk more values by single %pOF? Would the output be human
> readable without any delimiters or words around?

The delimiter is ':'. What comes to users, quick grepping tells the only
users are actually the unit tests, and this is also present in the
documentation.

Based on that I think we can safely omit that on %pfw actually. I thought
it was actually used somewhere.

-- 
Kind regards,

Sakari Ailus
sakari.ailus@...ux.intel.com