Re: SOLVED: mesh SCSI bus locks hard on 7500 when burning a CD-R in dao mode

On Sat, Feb 03, 2001 at 03:19:18PM +1100, Paul Mackerras [off-list ref] wrote:

Daniel Eisenbud writes:

[...]

As I said, it's been a while, and what I don't remember is whether the
mesh gives you a phase mismatch interrupt if you tell it to receive
data (do an IN operation) when the target also expects to receive data
(i.e. do an OUT operation).  I have a vague idea that it might do so
in PIO mode but not in DMA mode or something.  It's quite believable
that the whole thing would lock up in this situation.

Ah.

quoted

There are still some issues outstanding:
1)	The same table is duplicated in five or six drivers.  I think it
would make lots of sense to have a macro for the case statment in just
one place.  Should it go in scsi.h?  Or its own new file?

Well, it could be declared in scsi.h but the actual table of values
should go in a .c file.

My current patch has a static function in the new file scsi_dataout.h,
which is included by all the drivers in question.   But I agree that it
would be cleaner to declare the function in scsi.h, change
scsi_dataout.h to scsi_dataout.c, make the function no longer static,
and tell make about the dependencies.  I'll do that.

quoted

3)	It continues to be worrisome that the mesh driver doesn't handle
aborts right or retry lost arbitration (nor does mac53c94.)  Is there
anywhere that the way to do these things is documented?  I'm willing to
try my hand at fixing them.

I was never sure exactly how the higher levels of the scsi code
expected the host adaptor drivers (like mesh.c) to do aborts.  At the
time I tried to read the code but I found it to be quite opaque; it
was very complicated and not very well structured.  I haven't looked
at it lately, although I know Alan Cox was trying to tidy it up a bit
at one stage.

I'll take a look...

I thought the mesh driver did retry lost arbitration though.

The comment at the top of the file says that it doesn't, but that's as
far as I've investigated so far.  It may be that you just didn't get
around to changing the comment?

If you want to try to fix the problems and implement the aborts and
resets properly, that would be great.  You would at least need a copy
of the SCSI-2 standard (or at least a late draft) plus the "Macintosh
Technology in CHRP" document.

Are these available on the net, or would I have to order paper copies
from somewhere?

quoted

A quick patch will follow in the morning, and based on people's opinions
about issue 1 above, I'll make a more definitive patch to send to Linus
and Alan Cox and whoever one sends these things to.

I would very much like to see the proposed patches before they are
sent to Linus & Alan.

I'll be glad to show them to you first.

-Daniel

--
Daniel E. Eisenbud
eisenbud@cs.swarthmore.edu

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