silicon image 3124 data corruption with siis driver (10.0 RELEASE, GENERIC)

[David Cross]

Recently got a silicon image 3124 card to upgrade my Sun Ultra 10 to let it
support SATA drives effectively.  Put the card in and gave a couple of
tests.  fscked a 1T filesystem with ~30 million files.  No problems,
mounted the filesystem and did a checksum of a subdirectory to hundreds of
FS errors (looking for blocks well outside of the partition).  Unmounted,
redid fsck.  fine.  Redid fsck while doing a 'dd if=/dev/ada1 of=/dev/null'
and the fsck instantly died with unexpected errors.

Next I did a 'dd if=/dev/ada1 bs=126b count=8192 | sha256' got an answer,
re-ran it and got the same answer.  reran again while running another dd
if=/dev/ada1 bs=126b of=/dev/null in a different terminal and received a
different sha256 sum. Kept repeating it and getting different answers.
Killed the background dd and received the first answer again.

Tried with and without MSI; also tried to fall back and use the
ata-siliconimage driver, that one fails to attach (I believe its failing on
the LINEAR map, but very hard to tell given there isn't a specific error
message in that part of the driver).

I repeated this with 2 different cards in an U10 and a U5; these are stock
machines, nothing else in them other than this card; I can get a boot
verbose later, but this is really a vanilla config.