USB transfer coherency problems with write-allocate caches

[M. Warner Losh]

In message: <47A095D5.2060801 at semihalf.com>
            Rafal Jaworowski <raj at semihalf.com> writes:
: Doing a BUS_DMASYNC_PREREAD in usbd_start_transfer() fixes the problems, see
: this patch:
: 
: http://people.freebsd.org/~raj/patches/misc/usbdi-bus_dma-fix.diff
: 
: I'd like to hear comments from people knowing other architectures if they have
: any comments/objections.

I think that this fix looks good to me...

Warner