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

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Message-ID: <2194247.ngWdBSP92t@avalon>
Date:	Tue, 11 Feb 2014 20:17:59 +0100
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Josh Cartwright <joshc@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	Grant Likely <grant.likely@...aro.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 Josh,

On Tuesday 11 February 2014 12:08:46 Josh Cartwright wrote:
> On Tue, Feb 11, 2014 at 06:20:49PM +0100, Laurent Pinchart wrote:
> > On Tuesday 11 February 2014 10:48:26 Josh Cartwright wrote:
> > > On Tue, Feb 11, 2014 at 03:55:35PM +0100, Laurent Pinchart wrote:
> > > > On Tuesday 11 February 2014 08:41:08 Josh Cartwright wrote:
> > > > > On Tue, Feb 11, 2014 at 01:36:51PM +0100, Laurent Pinchart wrote:
> [..]
> 
> > > 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.
> > 
> > I can assign the intermediate value to a variable before dereferencing it
> > and drop my of_match_node() patch if it makes everybody happier.
> 
> Assuming you also intend to handle the case of_match_node() may return
> NULL, or otherwise prevent the execution of this codepath when
> !CONFIG_OF, then, yes, that sounds good.

I'll condition the call of that function to IS_ENABLED(CONFIG_OF), yes.

> It sure would be convenient if platform_device had a 'const struct
> of_device_id *of_id_entry' member similar to the existing struct
> platform_device_id one, that was set up during platform device matching.
> Most platform_driver users of of_match_node() would simply go away.

There's definitely room for improvement (although in this particular case the 
driver handles an I2C device, not a platform device).

I've always been slightly bothered by the duplication of matching information 
between native/legacy device IDs and OF device IDs. I haven't really given 
this a thought though, but I believe something should be done.

I've just remembered that, in the I2C case, the I2C core selects the 
appropriate i2c_device_id matching entry based on the compatible string, 
provided that the i2c_device_id table matches the of_device_id table with I2C 
device names set to the OF compatible string with the vendor prefix stripped 
off. Just food for thought.

-- 
Regards,

Laurent Pinchart

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