The patch described by the following excerpt from ChangeLog-2.6.22 makes
it impossible to use UDMA on a Tyan S2707 motherboard (SvrWks CSB5):

commit 2d5eaa6d
Author: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Date:   Thu May 10 00:01:08 2007 +0200

    ide: rework the code for selecting the best DMA transfer mode (v3)

    ...

This one-line patch against 2.6.23 fixes the problem.
Signed-off-by: NTony Battersby <tonyb@cybernetics.com>
Signed-off-by: NBartlomiej Zolnierkiewicz <bzolnier@gmail.com>