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    SubjectRe: [linux-usb-devel] Re: highmem and usb [was "sr: unalignedtransfer" in 2.5.2-pre1]
    On Wed, 2 Jan 2002, Jens Axboe wrote:

    > 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
    > highmem.

    Probably for a long time they'll be the only ones.
    All the char drivers will mainly do a copy_to/from_user
    or want memory they can manipulate directly.

    Regards
    Oliver


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