linux-kernel - Re: [PATCH] of: Turn of_match_node into a static inline when CONFIG

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Date:	Mon, 17 Feb 2014 18:19:53 +0000
From:	Grant Likely <grant.likely@...aro.org>
To:	Josh Cartwright <joshc@...eaurora.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH] of: Turn of_match_node into a static inline when CONFIG_OF isn't set

On Tue, 11 Feb 2014 10:48:26 -0600, Josh Cartwright <joshc@...eaurora.org> wrote:
> On Tue, Feb 11, 2014 at 03:55:35PM +0100, Laurent Pinchart wrote:
> > Hi Josh,
> > 
> > On Tuesday 11 February 2014 08:41:08 Josh Cartwright wrote:
> > > On Tue, Feb 11, 2014 at 01:36:51PM +0100, Laurent Pinchart wrote:
> > > > when CONFIG_OF is disabled of_match_node is defined as a macro that
> > > > evaluates to NULL. This breaks compilation of drivers that dereference
> > > > the function's return value directly. Fix it by turning the macro into a
> > > > static inline function that returns NULL.
> > > 
> > > Just this past week I did the same thing, but noticed that it breaks the
> > > following usecase:
> > > 
> > > 	#ifdef CONFIG_OF
> > > 	static const struct of_device_id foobar_matches[] = {
> > > 		{ .compatible = "foobar,whatsit", },
> > > 		{ },
> > > 	};
> > > 	#endif
> > > 
> > > 	static int probeme(struct platform_device *pdev)
> > > 	{
> > > 		struct of_device_id *id;
> > > 
> > > 		id = of_match_node(foobar_matches, pdev->dev.of_node);
> > > 		if (id) {
> > > 			/* ... */
> > > 		}
> > > 		return 0;
> > > 	}
> > > 
> > > When !CONFIG_OF and with your change, this will fail to build due to
> > > foobar_matches being undefined.
> > 
> > Good point. What would you think about
> > 
> > #define of_match_node(_matches, _node)  ((const struct of_device_id *)NULL)
> 
> I've just sent out a patchset that cleans up at least a couple of users
> that directly do of_match_node(matches, np)->data using
> of_find_matching_node_and_match.  Not sure if that will fix the usage
> you have in mind, though.
> 
> I am a bit weary about having an of_match_node() user that both directly
> dereferences the result (i.e. of_match_node(matches, np)->data) _and_
> builds when !CONFIG_OF; most likely due to a traumatic childhood event
> where demons flew out my nose.

As is supposed to happen when code dereferrences pointers blindly.

g.

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