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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:
    > > > 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.
    >
    > Once the capability is there, it'll find other uses. But allowing
    > them is not the same as requiring them. Getting rid of the current
    > model would break every USB driver, rather than just ones that want to
    > support highmem.

    So? Either you want to fix this now, or leave it that way forever. Just
    IMO of course, but you might as well just make a clean break.

    > > > - Add some kind of "page + offset" addressing model.
    > >
    > > Yes
    > >
    > > > 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.
    >
    > A bit of a delay would make things a bit easier ... :) Of course, if
    > scatterlist->address doesn't work any more, it won't matter much.

    A bit of delay will only make things worse, afaics.

    --
    Jens Axboe

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