On Thu, 2007-08-16 at 10:20 -0700, Randy Dunlap wrote:
> > For DMA transfers ... which is where you give the device a bus physical
> > address and a length and tell it to go off and perform the transfer on
> > its own, you need to use the dma_map_ functions.
> >
> > For PIO transfers, which are usually ones where you have to feed the
> > data into a special device register, since the kernel needs access to do
> > this, it has to be done via kmap_atomic()/kunmap_atomic(). So, if
> > everything has to go via pio, you use a sequence like
>
> Thanks for the confirmation.
>
> > scsi_for_each_sg(cmd, sg, max, i) {
> > offset = sg->offset;
> > len = sg->len;
> ->length;
>
> > do {
> > coffset = offset; clen =len;
> > buf = scsi_kmap_atomic_sg(sg, 1, &coffset, &clen)
>
> why 1 ?
You're mapping a single segment at a time to do the PIO.
> > offset -= coffset; clen -= len;
>
> += ?
>
> > <feed buf+coffset to/from PIO for clen>
> > scsi_kunmap_atomic_sg(buf);
> > } while (len > 0);
> > }
>
James
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