linux-kernel - Re: [PATCH] iommu: Remove stub functions for !CONFIG_IOMMU

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Date:	Mon, 29 Aug 2011 16:21:54 +0300
From:	Ohad Ben-Cohen <ohad@...ery.com>
To:	"Roedel, Joerg" <Joerg.Roedel@....com>
Cc:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	Stepan Moskovchenko <stepanm@...eaurora.org>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Brown <davidb@...eaurora.org>
Subject: Re: [PATCH] iommu: Remove stub functions for !CONFIG_IOMMU_API

On Mon, Aug 29, 2011 at 4:05 PM, Roedel, Joerg <Joerg.Roedel@....com> wrote:
> So in this case you can skip this whole part when CONFIG_IOMMU_API is
> disabled

Sure, we can do something like this in the driver:

#ifdef CONFIG_IOMMU_API

int do_the_iommu_thing(..)
{
   ... call the IOMMU API as needed...
}

#else

int do_the_iommu_thing(..)
{
    return 0;
}

#endif

Essentially, this means implementing the !CONFIG_IOMMU_API stubs in the driver.

Possible of course, but I think it's a bit neater to have that in one
place, where all drivers can use. Similar to !CONFIG_HWSPINLOCK,
!CONFIG_DEBUG_FS, ...

> This saves you even more .text size, no?

Not sure; I expect the code to be compiled out today when the IOMMU
API is called and CONFIG_IOMMU_API is not set.
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