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

[Jens Axboe <axboe@suse.de>]

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