Re: [V4 PATCH 3/6] pci: Generic function for setting up PCI device DMA coherency

[Russell King - ARM Linux]

On Wed, May 20, 2015 at 07:00:25AM -0500, Suravee Suthikulanit wrote:
> On 5/20/2015 4:34 AM, Catalin Marinas wrote:
> >We have a dummy of_dma_configure() already when !CONFIG_OF, otherwise
> >we would need #ifndef here. I already replied, I think for other
> >architectures we need this check to avoid a useless host->of_node test.
> 
> It seems that there are several places that have similar check. Would it be
> good to convert this into a macro? Something like:
> 
> #define OF_NODE_ENABLED(dev)	(IS_ENABLED(CONFIG_OF) && dev->of_node)

This /could/ be a useful compile-time optimisation: when CONFIG_OF is
disabled, dev->of_node exists but will always be NULL - but the
compiler doesn't know this.  Your suggestion above would tell the
compiler that when CONFIG_OF is disabled, OF_NODE_ENABLED() will
evaluate to a constant false, which means it can eliminate code.

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