linux-kernel - Re: [PATCH v3 1/6] device property: Helper to match multiple connections

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Message-ID: <YiIZoyfsJDcwR4gr@smile.fi.intel.com>
Date:   Fri, 4 Mar 2022 15:52:35 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Daniel Scally <djrscally@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-usb@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Subject: Re: [PATCH v3 1/6] device property: Helper to match multiple
 connections

On Fri, Mar 04, 2022 at 03:41:33PM +0200, Sakari Ailus wrote:
> On Fri, Mar 04, 2022 at 02:54:21PM +0200, Andy Shevchenko wrote:
> > On Thu, Mar 03, 2022 at 02:33:46PM -0800, Bjorn Andersson wrote:

...

> > > +		if (count >= matches_len && matches) {
> > > +			fwnode_handle_put(ep);
> > > +			return count;
> > > +		}
> > 
> > Wouldn't be the same as
> > 
> > 		if (count >= matches_len) {
> > 			fwnode_handle_put(ep);
> > 			break;
> > 		}
> 
> Don't you need to check for non-NULL matches here?

Right, this should be kept as in original patch.

> I find return above easier to read.

Okay, original code may work, so I have no strong opinion about return vs
break, although I find slightly better to have a single point of return in
such case.

> > ?

...

> > > +	count_graph = fwnode_graph_devcon_matches(fwnode, con_id, data, match,
> > > +						  matches, matches_len);
> > 
> > > +	matches += count_graph;
> > > +	matches_len -= count_graph;
> > 
> > No, won't work when matches == NULL.
> > 
> > Also, matches_len is expected to be 0 in that case (or at least being ignored,
> > check with vsnprintf() behaviour in similar case).
> > 
> > So, something like this, perhaps
> > 
> > 	if (matches && matches_len) {
> > 		matches += count_graph;
> > 		matches_len -= count_graph;
> > 	}
> 
> Good find!

I have checked vsnprintf() and indeed, it expects to have the size is 0 when
the resulting buffer pointer is NULL, and it doesn't do any additional checks.

> > > +	count_ref = fwnode_devcon_matches(fwnode, con_id, data, match,
> > > +					  matches, matches_len);

-- 
With Best Regards,
Andy Shevchenko