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    SubjectRe: [linux-usb-devel] Re: highmem and usb [was "sr: unaligned transfer" in 2.5.2-pre1]
    On Wed, Jan 02 2002, David Brownell wrote:
    > > > requirement for drivers is that the transfer buffers can be passed to
    > > > pci_map_single() calls by the Host Controller Drivers (HCDs). The
    > > > device drivers, and URBs, don't expose such mappings, they only
    > > > require that they can be created/destroyed.
    > >
    > > .. which is the requirement that you want to change to use pci_map_page
    > > or pci_map_sg
    > OK, I think I'm clear on this much then: in 2.5, to support block drivers
    > over USB (usb-storage only, for now) there needs to be an addition to
    > the buffer addressing model in usbcore, as exposed by URBs.
    > - Current "transfer_buffer" + "transfer_buffer_length" mode needs to
    > stay, since most drivers aren't block drivers.

    Why? Surely USB block drivers are not the only ones that want to support

    > - Add some kind of "page + offset" addressing model.


    > Discussion of details can be taken off LKML, it'd seem. Though I'm
    > curious when the scatterlist->address field will vanish, making these
    > changes a requirement. Is that a 2.5.2 thing?

    Maybe 2.5.3, dunno for sure.

    > Also, I noticed that include/asm-sparc/pci.h doesn't include the
    > standard pci_map_page() call ... what's up with that? That surely
    > causes portability problems.

    It probably isn't up to snuff yet.

    Jens Axboe

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