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    SubjectRe: virt_to_page/pci_map_page vs. pci_map_single
    On Mon, Nov 03, 2003 at 12:48:42PM -0600, James Bottomley wrote:
    > Jamie> The Document/DMA-mapping.txt in 2.6.0-test9 says "To map a
    > Jamie> single region, you do:" and then shows pci_map_single. Is
    > Jamie> DMA-mapping.txt in need of patching?
    > Sounds like it needs an update.
    > Erm, I don't think so. pci_map_single() covers a different use case
    > from pci_map_page().
    > The thing pci_map_single() can do that pci_map_page() can't is cope with
    > contiguous regions greater than PAGE_SIZE in length (which you get
    > either from kmalloc() or __get_free_pages()). This feature is used in
    > the SCSI layer for instance.

    Does "pci_map_page(virt_to_page(addr))" handle contiguous regions of
    multiple pages? It seems like the i386 implementation will (assuming
    we're dealing with kmalloc'd memory). Although the semantics of
    map_single seem better to me than map_page, if I'm mapping a single
    "region" of multiple pages.

    > There has been talk of deprecating dma_map_single() in favour of
    > dma_map_sg() (i.e. make all transfers use scatter/gather and eliminate
    > dma_map_single() in favour of a single sg entry table) but nothing has
    > been done about it (at least as far as I know).
    > James

    Jamie Wellnitz
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