Re: [linux-usb-devel] Re: highmem and usb [was "sr: unaligned transfer" in 2.5.2-pre1]

David Brownell
2002-01-02T18:57:30Z

> > 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.

> > - 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.

- Dave

> > 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
>