linux-kernel - Re: [PATCH] drivers/core/of: Add symlink to device-tree from devices with an OF node

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Date:	Wed, 19 Nov 2014 15:49:13 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Rob Herring <robherring2@...il.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jeremy Kerr <jeremy.kerr@....ibm.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Olof Johansson <olof@...om.net>,
	Grant Likely <grant.likely@...aro.org>,
	Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] drivers/core/of: Add symlink to device-tree from devices with an OF node

On Wednesday 19 November 2014 08:45:58 Rob Herring wrote:
> > static inline struct device_node *dev_of_node(struct device *of_node)
> > {
> >         if (!IS_ENABLED(CONFIG_OF))
> >                 return NULL;
> >
> >         return dev->of_node;
> > }
> >
> > Adding the IS_ENABLED() in a lot of drivers isn't horrible, but we seem
> > to be doing it a lot.
> 
> I think you misread things. of_node is always present now, so it
> should always be NULL for !CONFIG_OF.
> 

No, I didn't misread it but I should have been clearer with the intention:
The idea is to tell the compiler that we know it will be NULL when CONFIG_OF
is unset, so it can optimize out all code that does

	struct device_node *dn = dev_of_node(dev);

	if (dn) {
		...
		/* complex code */
		...
	}

and we can avoid using an #ifdef or if(IS_ENABLED()) in the source to
compile out the DT-only sections of a driver.

	Arnd
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