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Date:      14 Apr 2001 11:30:59 +0200
From:      Matthias Andree <ma@dt.e-technik.uni-dortmund.de>
To:        freebsd-stable@freebsd.org
Subject:   FreeBSD 4.x refuses to use DMA on WDC31200F?
Message-ID:  <m3ae5jakvg.fsf@emma1.emma.line.org>

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Hi,

I recently noticed that FreeBSD 4.x (4.0-RELEASE, 4.2-RELEASE,
4.2-STABLE, currently 4.3-RC) refuses to use DMA to transfer data
to/from my Western Digital Caviar AC31200F. This drive is able to do
DMA1 or PIO3, for a reason I cannot see and that is neither mentioned in
ata(4) or in syslog, even sysctl -w hd.atamodes=dma,---,---,---, does
not change FreeBSD's mind.

A WDCAC420400D is used in DMA mode (UDMA/33). My system is boots and
mounts /, /usr and /var from a SCSI disk attached to a Tekram DC-390
(AMD PCscsiII/53C974).

That very same drive can be successfully used in DMA mode with NetBSD
1.5 (same machine) and Linux 2.2.19 (same board type/chipset), I've
never seen corruption on that drive with DMA.

The drive is attached to a VIA VT82C586B (Apollo MVP3) on a Tyan Trinity
100AT (S1590).

What causes FreeBSD's refusal to use DMA? Can I fix that? Can somebody
else fix that?

-- 
Matthias Andree

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