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

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Date:	Mon, 17 Feb 2014 20:50:34 +0100
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Grant Likely <grant.likely@...aro.org>
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

Hi Grant,

On Monday 17 February 2014 18:18:29 Grant Likely wrote:
> On Tue, 11 Feb 2014 13:36:51 +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.
> 
> Is it not more problematic that code is dereferencing the return value
> directly *without* checking to see if it is NULL first? I suppose it
> will cause a runtime oops on all platforms except no-mmu, but still.
> Compile time catches are better.

There should be no risk of oops if the of_match_ptr() call is guarded by a 
compiler (as opposed to preprocessor) IS_ENABLED(CONFIG_OF) check. Now, if the 
check is missing, we'll oops at runtime, but the problem already exists before 
this patch.

Anyway I've decided to drop this patch and use an intermediate variable.

> > Signed-off-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > ---
> > 
> >  include/linux/of.h | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/of.h b/include/linux/of.h
> > index 70c64ba..719e69f 100644
> > --- a/include/linux/of.h
> > +++ b/include/linux/of.h
> > @@ -560,7 +560,13 @@ static inline const char *of_prop_next_string(struct
> > property *prop,> 
> >  }
> >  
> >  #define of_match_ptr(_ptr)	NULL
> > 
> > -#define of_match_node(_matches, _node)	NULL
> > +
> > +static inline const struct of_device_id *of_match_node(
> > +	const struct of_device_id *matches, const struct device_node *node)
> > +{
> > +	return NULL;
> > +}
> > +
> > 
> >  #endif /* CONFIG_OF */
> >  
> >  #if defined(CONFIG_OF) && defined(CONFIG_NUMA)

-- 
Regards,

Laurent Pinchart

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