cam: big transfers

[Kenneth D. Merry]

On Wed, Apr 09, 2003 at 15:42:38 -0400, John S. Bucy wrote:
> 
> Is it possible to do large (>MAXPHYS) bus transfers from a userland process
> via cam?

Not currently, no.  You'd need to do some hacking around in
cam_periph_mapmem() to allow for larger buffers.  It actually checks
against DFLTPHYS (64K) at the moment, not MAXPHYS, since some adapters
(e.g. the Adaptec 1542) can't handle more than 17 S/G segments.

If you just need larger buffers, and not performance, you could malloc a
new kernel-space buffer to hold the user data.

If you want performance as well, you could try writing your own routine
that would map N pages from userland into the kernel, where N would be
greater than MAXPHYS/PAGE_SIZE.

If you just need say 256K transferred at a time, you could try bumping
MAXPHYS to that and changing cam_periph_mapmem() to check against MAXPHYS
as long as your hardware can support that.

Ken
-- 
Kenneth Merry
ken at kdm.org