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.TH "USB_BUFFER_MAP_SG" "9" "07 August 2003" "" ""
.SH NAME
usb_buffer_map_sg \- create scatterlist DMA mapping(s) for an endpoint
.SH SYNOPSIS
.sp
\fB
.sp
int usb_buffer_map_sg  (struct usb_device * \fIdev\fB, unsigned \fIpipe\fB, struct scatterlist * \fIsg\fB, int \fInents\fB);
\fR
.SH "ARGUMENTS"
.TP
\fB\fIdev\fB\fR
device to which the scatterlist will be mapped
.TP
\fB\fIpipe\fB\fR
endpoint defining the mapping direction
.TP
\fB\fIsg\fB\fR
the scatterlist to map
.TP
\fB\fInents\fB\fR
the number of entries in the scatterlist
.SH "DESCRIPTION"
.PP
Return value is either < 0 (indicating no buffers could be mapped), or
the number of DMA mapping array entries in the scatterlist.
.PP
The caller is responsible for placing the resulting DMA addresses from
the scatterlist into URB transfer buffer pointers, and for setting the
URB_NO_TRANSFER_DMA_MAP transfer flag in each of those URBs.
.PP
Top I/O rates come from queuing URBs, instead of waiting for each one
to complete before starting the next I/O.   This is particularly easy
to do with scatterlists.  Just allocate and submit one URB for each DMA
mapping entry returned, stopping on the first error or when all succeed.
Better yet, use the usb_sg_*() calls, which do that (and more) for you.
.PP
This call would normally be used when translating scatterlist requests,
rather than \fBusb_buffer_map\fR, since on some hardware (with IOMMUs) it
may be able to coalesce mappings for improved I/O efficiency.
.PP
Reverse the effect of this call with \fBusb_buffer_unmap_sg\fR.
.SH "ABOUT THIS DOCUMENT"
.PP
This documentation is free software; you can redistribute
it and/or modify it under the terms of the GNU General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later
version.
.PP
This program is distributed in the hope that it will be
useful, but WITHOUT ANY WARRANTY; without even the implied
warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
See the GNU General Public License for more details.
.PP
You should have received a copy of the GNU General Public
License along with this program; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
MA 02111-1307 USA
.PP
For more details see the file COPYING in the source
distribution of Linux.
.PP
If you have comments on the formatting of this manpage, then please contact
Michael Still (mikal@stillhq.com).
.PP
This documentation was generated with kernel version 2.6.0.