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 09:39:36 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
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 Wed, Nov 19, 2014 at 8:49 AM, Arnd Bergmann <arnd@...db.de> wrote:
> 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.

Oh, right. That would definitely be worthwhile to do.

Rob
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