Re: ide-io.c, ide_do_request -- race condition?

[Jens Axboe <axboe@suse.de>]

On Fri, Jul 16 2004, Max T. Woodbury wrote:
> "Eric D. Mudama" wrote:
> > 
> > On Mon, Jul 12 at 13:52, Max T. Woodbury wrote:
> > >Still, why would PIO mode be unsafe?  (I can see slower, but I don't
> > >expect speed from this beast.  Oh well.  Thanks for the pointer.)
> > 
> > PIO has no data integrity check, so bogus cables that glitch the data
> > will not be detected.  Not sure if that is what he was talking about,
> > but is definitely a problem for PIO.
> 
> Huh? Unless something major has changed since the last time I looked at
> DMA hardware (and it has been a few years), DMA uses the same transfer
> sequence from the devices point of view as PIO.  The fact that the 
> transfer is under the control of another device rather than a program 
> should be transparent to the target device.  Impedance mismatches,
> reflections and constructive and destructive interference caused by
> cable problems don't care about who's in control of the busses.
> 
> I can see a possible problem with cache consistency causing problems
> with PIO, but there are similar (abet in some sense inverted or
> reversed) problems with DMA.

Yes that's very clever of you. But read what Eric writes - PIO has no
data integrity check. DMA transfers are crc'ed so you know if something
goes bad between device and host in the data phase, with PIO you do not.

-- 
Jens Axboe