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SubjectRe: IDE tape and SMP
On Mon, 26 Oct 1998, Andre M. Hedrick wrote:

> Gadi,
>
> I know that you wrote the original source, and we both know that I am
> trying to play pick and learn in weeks and months what you did in years.
> The reality is that it will be a long time before I can move through the
> source like you and Mark can. So what will it take to get you to pick up
> an play again?

I'm thinking about the latest ide-tape + SMP problems; it's hard for
me to fix, as I'm not very familiar with 2.1.x SMP. Mark/Scott/Erik and
myself developed the drivers without access to SMP systems, and although
I upgraded to a SMP system very recently, unfortunately I was not able
to repeat the latest SMP problems on my system yet.

I can certainly imagine that the IDE tape driver is not SMP safe, though;
it was not designed to support 2.1.x fine-grained SMP, and as cli() doesn't
seem to actually disable interrupts on all processors when local interrupts
were already disabled, the prevention of race conditions on UP seems to no
longer work unmodified on 2.1.x SMP.

That can potentially explain the locking of the backup process in the
'D' state, as Matthew reported.

I currently don't have an explanation for the "DSC timeouts" and
"IRQ timeouts" problems, though. It seems as if the timeout function
is called pre-maturely, and reminds me of the problem which Geert
reported a while ago, in which the IDE driver timeout handler
was called before the intended expiry. We worked around that one by
replacing a "add_timer()" with "mod_timer()" in ide_do_request(),
but at this point no timer should have been active in the first place.

> Second, I will follow your suggested direction. As always, you will be
> needed to point out assumption follies until more knowledge is hammered
> into my skull.
>
> Just by chance, would you send me copies of any and all
> docs/whitepages/etc and or forward the locations where I can get them??
> I have piles of stuff already and my wife wants me to stop the piles, but
> to quote a silly movie......"MORE INPUT, MORE INPUT"........
>
>
> Cheers,
> Andre Hedrick
> The IDE-FNG for Linux
> The APC UPS Specialist for Linux
>
> http://www.dyer.vanderbilt.edu/server/udma/
> http://www.dyer.vanderbilt.edu/server/apcupsd/ BINARIES

The IDE/ATAPI specifications are availabe on ftp://fission.dt.wdc.com,
under /pub/standards:

IDE ATA DISK: ata/ata-2/0948dr3.doc
IDE/ATAPI FLOPPY: SFF/specs/8070ir11.pdf
IDE/ATAPI CDROM: SFF_atapi/spec/SFF8020-r2.6/PDF/8020r26.pdf
IDE/ATAPI TAPE: QIC/QIC157/QIC157D.ZIP

DSC overlap is described in QIC157, while ATAPI overlap is described
in SFF8020. Linux currently doesn't support ATAPI overlap, but to
date I received just a single report of an ATAPI device which actually
implements it.

Gadi


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