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    SubjectRe: [PATCH 18 of 38] x86: unify pci iommu setup and allow swiotlb to compile for 32 bit
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    On Mon, 2008-11-17 at 12:48 +0900, FUJITA Tomonori wrote:
    > On Thu, 13 Nov 2008 11:10:16 -0800
    > Jeremy Fitzhardinge <jeremy@goop.org> wrote:
    >
    > > swiotlb on 32 bit will be used by Xen domain 0 support.
    >
    > If you want swiotlb on 32 bit, you need more modifications, I think.

    Possibly. It currently "Works For Me(tm)", but I should check it over.

    > For example, the following code assumes that the mask needs to be
    > 64 bits.

    The use of unsigned long for the mask is throughout the API and not
    simply limited to swiotlb.c. All the callers of dma_set_seg_boundary
    (PCI and SCSI subsys it seems) do not use a value >4G anywhere I can
    see. Presumably if something was we would see "warning: overflow in
    implicit constant conversion" somewhere along the line. If no value is
    set then the default is 0xffffffff which is safe on 32 bit.

    I suspect that even with PAE addresses above 4G aren't seen very often
    due to pre-existing subsystem specific bounce buffers or other existing
    limitations (like network buffers being in lowmem).

    Perhaps dma_addr_t should be used though?

    Ian.

    >
    > static void *
    > map_single(struct device *hwdev, char *buffer, size_t size, int dir)
    > {
    > unsigned long flags;
    > char *dma_addr;
    > unsigned int nslots, stride, index, wrap;
    > int i;
    > unsigned long start_dma_addr;
    > unsigned long mask;
    > unsigned long offset_slots;
    > unsigned long max_slots;
    >
    > mask = dma_get_seg_boundary(hwdev);
    > start_dma_addr = virt_to_bus(io_tlb_start) & mask;
    >
    > offset_slots = ALIGN(start_dma_addr, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
    > max_slots = mask + 1
    > ? ALIGN(mask + 1, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT
    > : 1UL << (BITS_PER_LONG - IO_TLB_SHIFT);
    >



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