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Date:      Sun, 24 Sep 2006 08:40:34 +1000
From:      "Jan Mikkelsen" <janm@transactionware.com>
To:        "'Stefan Esser'" <se@FreeBSD.org>, "'Scott Long'" <scottl@samsco.org>
Cc:        freebsd-stable@freebsd.org
Subject:   RE: Patch: sym(4) "VTOBUS FAILED" panics on amd64, amd64/89550
Message-ID:  <001701c6df61$48504640$0202a8c0@transactzbkv04>
In-Reply-To: <4514206A.8030601@FreeBSD.org>

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Stefan Esser wrote:
> I've been the co-author of the ncr SCSI driver, on which sym is based
> (though not that particular code fragment). Since I know the structure
> and principals of the driver (and since I have and know the docs up to
> the 53c875, possibly also the 53c895), I'd probably be in a position
> to work on this with the least effort to get started. Only problem is
> that I do not have an amd64 system for testing ...
>=20
> I changed the private allocator in the sym driver to use contigmalloc,
> some time ago, but now I understand that there are stricter alignment
> requirements. For a start, a work-around could be committed,=20
> IMHO (even
> if it is ugly). The better approach is of course an extension=20
> of busdma
> to support aligned physical chunks as required by the driver.
>=20
> But I could also try to find a clean fix for the affected driver code.

What are the "stricter alignment requirements" you have seen?  The only =
ones
I have seen are those on virtual addresses caused by the buddy =
allocator.
Replacing that would remove the virtual address alignment requirements,
unless I've missed something else.

Are there special physical alignment requirements that the driver is not
currently meeting?

> Is the Symbios SCSI controller still used that much that the effort
> required for a "clean" fix is well spent?

This is a broader question.  For my immediate purposes, my patch and =
wasting
a few pages gets a functional tape drive, which is a reasonable tradeoff =
to
me.  I don't know how anyone else feels.  This does seem to have been =
broken
on amd64 for a while and I haven't seen a large number of messages
complaining.

However:  I needed an inexpensive SCSI controller for a machine, looked =
at
the supported hardware list, and bought a sym(4) controller.  It didn't
work.  I think either the driver or the supported hardware list should =
be
fixed;  my preference is the driver.

Regards,

Jan.




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