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    SubjectRe: [PATCH] iommu: Remove stub functions for !CONFIG_IOMMU_API
    On Mon, Aug 29, 2011 at 09:21:54AM -0400, Ohad Ben-Cohen wrote:
    > On Mon, Aug 29, 2011 at 4:05 PM, Roedel, Joerg <Joerg.Roedel@amd.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.

    I expect only very few drivers need that. Most drivers (like KVM and the
    upcoming VFIO) rely on the iommu-api and I expect most other drivers
    using the directly will also rely on an iommu. So this change makes
    still sense to me.

    > 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.

    But you even save all code that would use the iommu-api in your driver.
    This change forces you to compile out this code too leading to smaller
    .text-size.

    Joerg

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