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    SubjectRe: [PATCH 4/7] swiotlb: Allow arch override of address_needs_mapping
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    On Wed, 08 Apr 2009 14:55:55 -0700
    Jeremy Fitzhardinge <jeremy@goop.org> wrote:

    > FUJITA Tomonori wrote:
    > > On Wed, 8 Apr 2009 15:56:32 -0500
    > > Kumar Gala <galak@kernel.crashing.org> wrote:
    > >
    > >
    > >> On Apr 8, 2009, at 3:38 PM, Christoph Hellwig wrote:
    > >>
    > >>
    > >>> On Wed, Apr 08, 2009 at 09:09:18AM -0500, Kumar Gala wrote:
    > >>>
    > >>>> From: Becky Bruce <beckyb@kernel.crashing.org>
    > >>>>
    > >>>> Some architectures require additional checking to determine
    > >>>> if a device can dma to an address and need to provide their
    > >>>> own address_needs_mapping..
    > >>>>
    > >>> Shouldn't we just move it completely to the arch? I think that ia64
    > >>> and
    > >>> x86 currently use the same one is more of an accident.
    > >>>
    > >> It seems like the swiotlb code uses __weak for a number of things:
    > >>
    > >> lib/swiotlb.c:void * __weak __init swiotlb_alloc_boot(size_t size,
    > >> unsigned long nslabs)
    > >> lib/swiotlb.c:void * __weak swiotlb_alloc(unsigned order, unsigned
    > >> long nslabs)
    > >> lib/swiotlb.c:dma_addr_t __weak swiotlb_phys_to_bus(struct device
    > >> *hwdev, phys_addr_t paddr)
    > >> lib/swiotlb.c:phys_addr_t __weak swiotlb_bus_to_phys(struct device
    > >> *hwdev, dma_addr_t baddr)
    > >> lib/swiotlb.c:void * __weak swiotlb_bus_to_virt(struct device *hwdev,
    > >> dma_addr_t address)
    > >> lib/swiotlb.c:int __weak swiotlb_arch_address_needs_mapping(struct
    > >> device *hwdev,
    > >> lib/swiotlb.c:int __weak swiotlb_arch_range_needs_mapping(phys_addr_t
    > >> paddr, size_t size)
    > >>
    > >> instead of #ifndef HAVE_ARCH_<FOO>. Not sure if there is a historical
    > >> reason for that.
    > >>
    > >
    > > ia64 and x86_64 use swiotlb but neither need this function. And
    > > neither need any above __weak. They were added for dom0 support.
    > > Yeah, swiotlb is much cleaner and better if we don't add dom0 support.
    > >
    >
    > Some architectures need non-trivial bus<->phys conversion routines, etc,

    Only Xen needs such conversion for swiotlb.


    > so either we can require it that all architectures wishing to use
    > swiotlb define these functions, or have weak default functions that can
    > be overridden by architectures where necessary.

    Can you give an example? I don't think IA64, X86_64 or POWER (which
    will use swiotlb) need any __weak functions. If you say other archs
    could use swiotlb, please tell me how they need these __weak.


    > This isn't a specific Xen dom0 requirement, except that enabling it in

    Yes, it is.


    > the config will override these functions (but now in a Xen-only file,
    > rather than affecting the normal x86 pci-swiotlb.c).

    And again, x86' pci-swiotlb is much cleaner without dom0 support.


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