ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=xxx

FreeBSD 6.0-CURRENT with GENERIC kernel built 27th Sep.
On a SunBlade 100 I see these messages regularly when
dma is enabled. The messages go away when I either use
atacontrol to set the mode to PIO4 or set hw.ata.ata_dma to 0
I do get data corruption on the disk if left in DMA mode.

dmesg:

GDB: no debug ports present
KDB: debugger backends: ddb
KDB: current backend: ddb
Copyright (c) 1992-2004 The FreeBSD Project.
Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
        The Regents of the University of California. All rights reserved.
FreeBSD 6.0-CURRENT #0: Mon Sep 27 14:47:16 CST 2004
    xxx_at_xxx.xxx:/usr/obj/usr/src/sys/GENERIC
WARNING: WITNESS option enabled, expect reduced performance.
Timecounter "tick" frequency 502000000 Hz quality 0
real memory  = 671088640 (640 MB)
avail memory = 641736704 (612 MB)
cpu0: Sun Microsystems UltraSparc-IIe Processor (502.00 MHz CPU)
nexus0: <Open Firmware Nexus device>
pcib0: <U2P UPA-PCI bridge> on nexus0
pcib0: Sabre (US-IIe) compatible, impl 0, version 0, ign 0x7c0, bus A
pcib0: [FAST]
pcib0: [GIANT-LOCKED]
pcib0: [FAST]
pcib0: [GIANT-LOCKED]
pcib0 dvma: DVMA map: 0xc0000000 to 0xc3ffffff
pci0: <OFW PCI bus> on pcib0
ebus0: <PCI-EBus3 bridge> mem 0xf1000000-0xf17fffff,0xf0000000-0xf0ffffff at device 12.0 on pci0
ebus0: <idprom>: incomplete
ebus0: <flashprom> addr 0-0xfffff (no driver attached)
eeprom0: <EEPROM/clock> addr 0x100000000-0x100001fff on ebus0
eeprom0: model mk48t59
eeprom0: hostid 830de054
isab0: <PCI-ISA bridge> at device 7.0 on pci0
isa0: <ISA bus> on isab0
gem0: <Sun ERI 10/100 Ethernet Adaptor> mem 0x400000-0x41ffff at device 12.1 on pci0
miibus0: <MII bus> on gem0
ukphy0: <Generic IEEE 802.3u media interface> on miibus0
ukphy0:  10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, auto
gem0: 2kB RX FIFO, 2kB TX FIFO
gem0: Ethernet address: 00:03:ba:0d:e0:54
gem0: if_start running deferred for Giant
gem0: [GIANT-LOCKED]
fwohci0: <1394 Open Host Controller Interface> mem 0x422000-0x4227ff,0x420000-0x4207ff at device 12.2 on pci0
fwohci0: Could not allocate irq
device_attach: fwohci0 attach returned 6
pci0: <serial bus, USB> at device 12.3 (no driver attached)
pci0: <old, non-VGA display device> at device 3.0 (no driver attached)
pci0: <multimedia, audio> at device 8.0 (no driver attached)
atapci0: <AcerLabs Aladdin UDMA66 controller> port 0xa20-0xa2f,0xa08-0xa0b,0xa10-0xa17,0xa18-0xa1b,0xa00-0xa07 at device 13.0 on pci0
ata2: channel #0 on atapci0
ata3: channel #1 on atapci0
pci0: <display, VGA> at device 19.0 (no driver attached)
pcib1: <OFW PCI-PCI bridge> at device 5.0 on pci0
pci1: <OFW PCI bus> on pcib1
fxp0: <Intel 82550 Pro/100 Ethernet> port 0x1000-0x103f mem 0x4020000-0x403ffff,0x4000000-0x4000fff at device 1.0 on pci1
miibus1: <MII bus> on fxp0
inphy0: <i82555 10/100 media interface> on miibus1
inphy0:  10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, auto
fxp0: Ethernet address: 00:02:b3:32:6a:c7
fxp1: <Intel 82550 Pro/100 Ethernet> port 0x1040-0x107f mem 0x4040000-0x405ffff,0x4002000-0x4002fff at device 2.0 on pci1
miibus2: <MII bus> on fxp1
inphy1: <i82555 10/100 media interface> on miibus2
inphy1:  10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, auto
fxp1: Ethernet address: 00:02:b3:3c:94:a4
Timecounters tick every 10.000 msec
ad0: 14594MB <ST315310A/3.28> [29651/16/63] at ata2-master UDMA66
acd0: CDRW <LTN486S/YSU1> at ata2-slave PIO4
ata3-master: DMA limited to UDMA33, non-ATA66 cable or device
ad1: 39266MB <IBM-DTLA-305040/TW4OA60A> [79780/16/63] at ata3-master UDMA33
Mounted root from ufs:/dev/ad0a.