Re: [Ocf-linux-users] OCF Talitos driver - DMA alignment

[David M. <dav...@mc...>]

Jivin Kim Phillips lays it down ...
> On Tue, 11 May 2010 13:22:38 +0300
> avital sela <avi...@gm...> wrote:
> 
> > Hi Kim,
> 
> Hi Avital,
> 
> > I'm working on an ocf driver for a custom made hw that does AES and SHA, and
> > uses DMA.
> > I've noticed that in your talitos driver you also used DMA but you never
> > checked for alignment, whereas in David's Safenet code he did check for
> > alignments.
> > My questions are:
> > 1. are you using a 1-byte aligned DMA, therefore you don't need alignment?
> 
> correct, talitos drives h/w that doesn't have alignment restrictions.


Yep,  it's purely a HW limitation,  some crypto devices can handle the
unaligned data and some can't.  Same thing in network driver land.

The solution is usually "bounce buffers" of some kind.

> > 2. or alternatively, is there some way to guarantee that buffers are 32bit
> > aligned beforehand?
> 
> In OCF-linux, both safe and hifn drivers look like they copy data to
> ensure alignment.

For most uses you will receive aligned data.  Some of the OCF drivers handle
unaligned data,  and some just fail the request.

> In the upstream kernel's crypto API, it looks like a crypto
> drivers' .cra_alignmask setting is used for this purpose.
> 
> [cc:ing ocf list in case there's something I'm missing.]

Nothing missing that I can see ;-)

Cheers,
Davidm

-- 
David McCullough,      dav...@mc...,  Ph:+61 734352815
McAfee - SnapGear      http://www.mcafee.com         http://www.uCdot.org